White light source system

ABSTRACT

According to one embodiment, there is provided a white light source system. P(λ), B(λ) and V(λ) satisfy an equation (1) below in a wavelength range of 380 nm to 780 nm. The white light source system satisfies an expression (2) below in a wavelength range of 400 nm to 495 nm:∫380780⁢P⁡(λ)⁢V⁡(λ)⁢d⁢⁢λ=∫380780⁢B⁡(λ)⁢V⁡(λ)⁢d⁢⁢λ(1)where P(λ) is a light emission spectrum of white light, B(λ) is a light emission spectrum of blackbody radiation of a color temperature correspond to a color temperature of the white light, and V(λ) is a spectrum of a spectral luminous efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/853,847, filed Apr. 21, 2020, which is a continuation of U.S.application Ser. No. 16/444,243, filed Jun. 18, 2019, now U.S. Pat. No.10,674,577, issued Jun. 2, 2020, which is a continuation of U.S.application Ser. No. 16/251,468, filed Jan. 18, 2019, now U.S. Pat. No.10,375,786, issued Aug. 6, 2019, which is a continuation of U.S.application Ser. No. 15/850,399, filed Dec. 21, 2017, now U.S. Pat. No.10,231,305, issued Mar. 12, 2019, which is a continuation ofInternational Application No. PCT/JP2016/068714, filed Jun. 23, 2016,which designated the United States, and claims the benefit of JapanesePatent Application No. 2015-126776, filed Jun. 24, 2015, and JapaneseApplication No. 2016-082968, filed Apr. 18, 2016, the entireties ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a white light source and a white lightsource system for use in illumination in which natural light equivalentto sunlight is required, for example, illumination for articles onexhibition in an art museum or the like, illumination for patients whoare forced to stay for long periods in a hospital or the like, andillumination in houses and offices where high color rendering isrequired.

BACKGROUND OF THE INVENTION

In works of art and craft, the colors that the works have are one of themost important characteristics. For example, a painting or a pot itselfdoes not emit light. Thus, in an art museum or the like, theillumination at a time of appreciating an article on exhibition is asimportant in meaning as the article itself. The reason for this is thata person who appreciates the article on exhibition observes that portionof the visible light radiated from an illumination light source that isreflected by the surface of the article. Even if an artist expressesvery beautiful colors, unless the light from the light source that isirradiated on the article on exhibition includes emission lightcomponents corresponding to specific colors, the person appreciating thearticle can only observe the article with tonality which is dark andpoor in color sensation.

The most desirable light source for this purpose of illumination issunlight. As sunlight is composed of consecutive wavelength componentsof light, the sunlight includes, substantially equally, all lightcomponents of visible light wavelengths from 400 nm to 780 nm, and canreproduce all colors existing in nature as original colors inherent tosubstances in nature. However, no matter how excellent the sunlight isas the light source, precious works of art, such as paintings, are notappreciated in an outdoor bright space, while such works of art aredirectly exposed to sunlight. The reason why the works of art are storedin a specific place such as an art museum and are appreciated is, inpart, because it is necessary to protect them from accidents such as bythe weather and sealing. However, a more important reason is that it isnecessary to protect the works of art from a great quantity ofirradiation.

This is because sunlight includes the visible light of all wavelengths,and also includes emission light components other than visible light,such as ultraviolet and infrared. In particular, since ultraviolet isstronger in energy than visible light, direct exposure to sunlightpromotes fading and embrittlement of historic paintings, etc. Thus, anartificial light source is needed. However, the artificial light sourceis required to be able to reproduce sunlight as correctly as possible,in addition to having such convenient features of artificial light thatthe amount of light is adjustable and the amount of ultraviolet isreduced as much as possible.

On the other hand, in recent years, as an artificial light source,attention has been paid to a light source using an LED (light-emittingdiode) from the standpoint of energy saving and reduction in emission ofcarbon dioxide. Compared to a conventional incandescent bulb using atungsten filament, the LED has a long lifetime and can achieve energysaving. Because of the convenience of the LED, LED illumination israpidly gaining in popularity in the market. In many types of LEDillumination in the early stage, white light was obtained by combining ablue light emitting LED and a yellow light emitting phosphor, and onlyunnatural white which lacks in warmth could be reproduced. However, withremarkable enhancement in performance in step with the increasingpopularity of LED products in the market, various improvements have beenmade to combinations of LEDs and phosphors. As a result, some whitelight sources that can reproduce sunlight have been developed.

Patent document 1 discloses an invention relating to a white lightsource having the same light emission spectrum as sunlight. Sunlightswith different color temperatures are reproduced with blackbodyradiation spectra of the same color temperatures. In this invention, awhite light source can be obtained which reproduces light close tosunlight of various color temperatures which vary with time, not onlywith respect to apparent white light but also with respect to thespectrum shape. Patent document 2 discloses an invention relating to anillumination system using a white light source, and relates to officeillumination or the like, with the object of illumination being mainly ahuman or the like. This system can adjust color temperature orilluminance of indoor light, while detecting a variation of outdoorlight. White light illumination corresponding to variations due tophysiological phenomena of humans and seasons can be obtained. Inaddition, patent document 3 discloses an invention relating to anartificial sunlight system in which a plural of light-emitting diodemodules with different color temperatures are combined. This system canreproduce variations of color temperatures of sunlight which is radiatedon places of different latitudes and longitudes on the earth.

CITATION LIST Patent Literature

Patent document 1: PCT International Publication No. 2012/144087

Patent document 2: Jpn. Pat. Appln. KOKAI Publication No. 2011-23339

Patent document 3: Jpn. PCT National Publication No. 2009-540599

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a light emission spectrum of sunlight in thedaytime in winter in Milan, Italy.

FIG. 2 is a graph showing a light emission spectrum of sunlight in theevening in spring in Tokyo, Japan.

FIG. 3 is a graph showing a light emission chromaticity region which awhite light source of the present invention exhibits.

FIG. 4 is a graph showing variations of a color temperature andilluminance of sunlight in a day in spring in Tokyo, Japan.

FIG. 5 is a graph showing light emission spectra of sunlight in themorning, daytime, and evening in spring in Yokohama, Japan.

FIG. 6 is a graph showing light emission spectra of the white lightsource of the present invention, the light emission spectra being areproduction of light emission spectra of sunlight in the morning,daytime, and evening in spring in Yokohama, Japan.

FIG. 7 is a graph showing a difference spectrum between a light emissionspectrum of a light source A and a blackbody radiation spectrum havingthe same color temperature.

FIG. 8 is a graph showing a difference spectrum between a light emissionspectrum of a light source B and a blackbody radiation spectrum havingthe same color temperature.

FIG. 9 is a graph showing a difference spectrum between a light emissionspectrum of a light source C and a blackbody radiation spectrum havingthe same color temperature.

FIG. 10 is a graph comparing spectral intensities of P(λ)V(λ) of thelight source C and B(λ)V(λ) of blackbody radiation having the same colortemperature.

FIG. 11 is a graph comparing spectral intensities of P(λ)V(λ) of thelight source B and B(λ)V(λ) of blackbody radiation having the same colortemperature.

FIG. 12 is a graph comparing spectral intensities of P(λ)V(λ) of thelight source A and B(λ)V(λ) of blackbody radiation having the same colortemperature.

FIG. 13 is a graph showing variations of a color temperature andilluminance of sunlight in a day in spring in Yokohama, Japan.

FIG. 14 is a graph showing a light emission spectral characteristic of awhite light source of Comparative Example 1,(P(λ)×V(λ)/(P(λmax1)×V(λmax1)).

FIG. 15 is a graph relating to a blackbody radiation spectrum of a colortemperature corresponding to the white light source of ComparativeExample 1, and presents B(λ)×V(λ)/(B(λmax2)×V(λmax2)).

FIG. 16 is a graph showing a difference spectrum between the white lightsource of Comparative Example 1 and the blackbody radiation spectrum ofthe corresponding color temperature.

FIG. 17 is a graph comparing spectral intensities of P(λ)V(λ) of thewhite light source of Comparative Example 1 and B(λ)V(λ) of blackbodyradiation having the same color temperature.

FIG. 18 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source (5) of Example 2 and B(λ)V(λ) of blackbody radiation havingthe same color temperature.

FIG. 19 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source (6) of Example 2 and B(λ)V(λ) of blackbody radiation havingthe same color temperature.

FIG. 20 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source (7) of Example 2 and B(λ)V(λ) of blackbody radiation havingthe same color temperature.

FIG. 21 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source (9) of a Comparative Example and B(λ)V(λ) of blackbodyradiation having the same color temperature.

FIG. 22 is a graph showing variations of a color temperature andilluminance of sunlight in a day in spring in Wakkanai (Hokkaido),Japan.

FIG. 23 is a graph showing variations of a color temperature andilluminance of sunlight in a day in summer in Taipei, Taiwan.

FIG. 24 is a graph showing variations of a color temperature andilluminance of sunlight in a day in summer in Los Angeles, the USA.

FIG. 25 is a graph showing variations of a color temperature andilluminance of sunlight in a day in autumn in Sakai (Osaka), Japan.

FIG. 26 is a graph showing variations of a color temperature andilluminance of sunlight in a day in winter in Naha (Okinawa), Japan.

FIG. 27 is a schematic view illustrating an example of a white lightsource system of an embodiment.

FIG. 28 is a schematic view illustrating a second example of the whitelight source system of the embodiment.

FIG. 29 is a cross-sectional view illustrating a first example of an LEDmodule used in the white light source system.

FIG. 30 is a cross-sectional view illustrating a second example of theLED module used in the white light source system.

FIG. 31 is a cross-sectional view illustrating a third example of theLED module used in the white light source system.

FIG. 32 is a cross-sectional view illustrating a fourth example of theLED module used in the white light source system.

FIG. 33 is a cross-sectional view illustrating a fifth example of theLED module used in the white light source system.

FIG. 34 is a graph showing a first example of a light emission spectrumand an excitation spectrum of a phosphor.

FIG. 35 is a graph showing a second example of the light emissionspectrum and excitation spectrum of the phosphor.

FIG. 36 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source (10) of a Comparative Example and B(λ)V(λ) of blackbodyradiation having the same color temperature.

FIG. 37 is a graph showing a reproduction region of color temperaturesby a white light source system of Example A.

FIG. 38 is a schematic view illustrating an LED module of the whitelight source system of Example A.

FIG. 39 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source 7 of Example A and B(λ)V(λ) of blackbody radiation havingthe same color temperature.

FIG. 40 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source 8 of Example A and B(λ)V(λ) of blackbody radiation havingthe same color temperature.

FIG. 41 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source 9 of Example A and B(λ)V(λ) of blackbody radiation havingthe same color temperature.

FIG. 42 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source 10 of Example A and B(λ)V(λ) of blackbody radiation havingthe same color temperature.

FIG. 43 is a plan view illustrating a phosphor layer in a white lightsource system of Example C.

FIG. 44 is a graph comparing spectral intensities of P(λ)V(λ) of a whitelight source 11 of Example A and B(λ)V(λ) of blackbody radiation havingthe same color temperature.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention is to provide an artificial lightsource system which is usable for an object that requires the samenatural illumination as sunlight, such as an article on exhibition in anart museum or the like, or an inpatient staying for a long time, thesystem being an illumination system which can reproduce light as closeas possible to sunlight, and can successively reproduce even finedifferences of sunlight varying from time to time and from place toplace.

In recent years, as shown in Patent Documents 1 to 3, some patentdocuments have proposed artificial light sources which can reproducesunlight. Aside from these, many products, whose main attraction isreproduction of sunlight, are on the market. Most of these illuminationproducts aim at providing light sources which emit light close tosunlight of a certain time instant, or aim at providing, even when avariation in sunlight is captured, light close to sunlight by payingattention to an apparent color temperature variation of sunlight. LikePatent Document 3 among others, there is a concept of controlling thecolor temperatures and optical characteristic variation data of sunlightdue to differences in time and place. In the case of Patent Document 3,however, as regards optical characteristic variations other than colortemperatures, no concrete description is given, nor is any improvementmade.

However, the variation of sunlight is not limited to the variation dueto the color temperature. For example, sunlight also varies due to aradiation rate, purity and turbidity. Subtle variations including theseelements in addition to the color temperature are major factors whichaffect different climates in different regions. For example, assumingthat Japan is divided into a Japan Sea side and a Pacific side, thereare many cloudy, rainy and snowy days in the Japan Sea-side region.Since the atmosphere contains much floating matter such as moisturevapor and dust, the sunlight becomes gloomy, and the colors of thingslook turbid. On the other hand, in the Pacific-side region, since thereis less moisture vapor, the purity of the atmosphere is high, and thingsappear in clear colors. Hence, there occur differences in taste ofcolors among regions, and there is a tendency that the people living onthe Japan Sea side favor turbid colors while the people living on thePacific side favor clear colors.

Works of art, such as paintings, are creations by humans. Accordingly,although the works of art are original works by individuals, it isinevitable that the color expressions, which the works have, areinfluenced by environments. In the case of a realistic painting, this isa matter of course. Even in the case of an abstract painting, it ispossible that the selection itself, such as emphasis on red, emphasis onblue, a liking for clear colors, or a liking for turbid colors, isalready influenced by climates, etc. Even if such selection is purelybased on personal sensitivity, the influence is inevitable as long asthe color expression of the created work is discerned by reflected lightfrom a light source. Specifically, even if the creator deliberatelyemphasized red, it is natural that the degree of emphasis is influencedby the amount of the red component of the same wavelength included inthe light of the light source.

Accordingly, in art appreciation or the like, in order to understand thereal value of the work of art, it is very important to reproduce notonly the natural light of the sun, but also the same photoenvironment aswhen the work was created. In other words, when a work of art isappreciated under the same light as the creator experienced, forexample, in the country or region where the work was created, or theseason, time, age, weather, etc., in which the work was created, itshould first become possible that the work is understandable in the sameposition as the creator.

The white light source of the present invention basically reproducessunlight of various color temperatures. Specifically, when sunlight of aspecific color temperature is reproduced, a blackbody radiation spectrumhaving the same color temperature as sunlight is regarded as a spectrumby rays of sunlight. In addition, the shape of the spectrum, too, isapproximated. The sun can be thought to be a kind of blackbody. There isa good agreement between a radiation spectral curve of a blackbody and alight emission spectrum curve of sunlight, and it is considered that thespectral distribution of the actual rays of the sun is close to ablackbody radiation spectrum of 5800 K.

However, the actual light emission spectrum of sunlight reaching theearth deviates slightly from the blackbody radiation spectrum. Thereason for this is that even if white light radiated from the sun isclose to the spectrum of blackbody radiation, the white light passesthrough a layer of air, moisture vapor and dust before reaching theearth, and light of a specific wavelength is scattered. A macroscopicvariation due to scattering of blue light, etc. can be coped with as avariation in color temperature, but it is difficult to artificiallyreproduce fine irregular waveforms occurring in a specific wavelengthregion of the light emission spectrum.

However, such fine differences are factors which make differences inclimate between regions. The present invention is devised so as to copewith even such fine differences. Specifically, as regards a differencebetween the spectrum of sunlight reaching the earth and the blackbodyradiation spectrum of the same color temperature as the sunlight, thedegree of this difference is converted to a deviation from a blackbodylocus, and white light of a correlated color temperature having apredetermined deviation is reproduced.

The white light source of the present invention reproduces fine colorvariations due to differences between regions as described above, andalso successively reproduces even the color temperature variations ofsunlight which varies from time to time, thus providing very naturalsunlight by an artificial light source. In addition, the white lightsource of this invention greatly reduces, compared to conventionalartificial light sources, light emission components of ultraviolet andblue light, which are regarded as being harmful to paintings and humanbodies. The merits of sunlight are adopted in all senses, and naturalwhite light is provided.

According to the embodiments, the following inventions can be provided.

[1] A white light source satisfying an expression:

−0.2≤[(P(λ)×V(λ))/(P(λmax1)×V(λmax1))−(B(λ)×V(λ))/(B(λmax2)×V(λmax2))]≤+0.2,

where P(λ) is a light emission spectrum of the white light source havinga correlated color temperature with a deviation duv from a blackbodyradiation locus being ±0.005 or less; B(λ) is a light emission spectrumof blackbody radiation of a color temperature correspond to the colortemperature of the white light; V(λ) is a spectrum of a spectralluminous efficiency; λmax1 is a wavelength at which P(λ)×V(λ) islargest; and λmax2 is a wavelength at which B(λ)×V(λ) is largest.

[2] The white light source of [1], wherein the white light source hascorrelated color temperatures in a range of 2600 to 6500 K.

[3] A white light source system including LED modules which are eachcomposed of the white light source of [1] or [2] and are configured toemit white light having at least two chromaticity points having a plusdeviation from a blackbody locus and at least two chromaticity pointshaving a minus deviation from the blackbody locus within a regionsurrounded by four kinds of chromaticity points with a deviation duvfrom white lights of two arbitrary kinds of color temperatures being±0.005 or less, and a controller configured to control light emissionintensities of the LED modules, the white light source system beingconfigured to be capable of obtaining white light in which emissionlights from at least four kinds of LED modules controlled to havearbitrary intensities are mixed.

[4] The white light source system of [3] including a database storingspectra of sunlight varying in accordance with variations with time inmajor regions at home and abroad, wherein light emission intensities ofthe plural of LED modules are controlled based on desired sunlightspectrum data in the database, and sunlight corresponding to a desiredtime of year in a desired region can be reproduced.

[5] The white light source system of [3] or [4], wherein the LED moduleincludes an LED and a phosphor layer, and the phosphor layer includes aphosphor and a resin.

[6] The white light source system of [5], wherein, in the white lightsource in which the LED is configured to emit primary light ofultraviolet to violet with a peak wavelength of 360 nm to 420 nm and thephosphor layer covering the LED is configured to absorb the primarylight from the LED and to emit secondary light of white, an intensity ofthe LED primary light emitted from the white light source is 0.4 mW/lmor less.

[7] The white light source system of [3] or [6], wherein the white lightsource system is used as illumination for a work of art and craftexhibited in an art museum, a museum or the like.

{1} A white light source system configured to be capable of reproducingwhite light of a color temperature on a locus of blackbody radiation,and white light of a correlated color temperature with a deviation fromthe blackbody locus,

wherein P(λ), B(λ) and V(λ) satisfy an equation (1) below in awavelength range in which λ is 380 nm to 780 nm, and the P(λ) and theB(λ) satisfy an expression (2) below in a wavelength range of 400 nm to495 nm:

$\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1) \\{{{P(\lambda)}/{B(\lambda)}} \leq {1.8.}} & (2)\end{matrix}$

where P(λ) is a light emission spectrum of white light emitted from thewhite light source system, B(λ) is a light emission spectrum ofblackbody radiation of a color temperature correspond to a colortemperature of the white light source system, and V(λ) is a spectrum ofa spectral luminous efficiency.

{2} The white light source system of {1}, wherein the white light sourcesystem is configured to be capable of reproducing white light of a colortemperature on the locus of the blackbody radiation, and white light ofany one of correlated color temperatures with a deviation from the colortemperature of the white light being in a range of ±0.005 duv.

{3} The white light source system of {2}, wherein the white light sourcesystem is configured to be capable of reproducing white light of a colortemperature of 2000 K to 6500 K on the locus of the blackbody radiation,and white light of any one of correlated color temperatures with adeviation from the color temperature of the white light being in a rangeof ±0.005 duv.

{4} The white light source system of any one of {1} to {3}, whichsatisfies an expression (3) below:

−0.2≤[(P(λ)×V(λ))/(P(λmax1)×V(λmax1))−(B(λ)×V(λ))/(B(λmax2)×V(λmax2))]≤+0.2,  (3)

where P(λ) is a light emission spectrum of white light emitted from thewhite light source system, B(λ) is a light emission spectrum ofblackbody radiation of a color temperature correspond to a colortemperature of the white light source system, and V(λ) is a spectrum ofa spectral luminous efficiency, λmax1 is a wavelength at which P(λ)×V(λ)is largest, and λmax2 is a wavelength at which B(λ)×V(λ) is largest.

{5} The white light source system of {4}, which satisfies an expression(4) below:

−0.1≤[(P(λ)×V(λ))/(P(λmax1)×V(λmax1))−(B(λ)×V(λ))/(B(λmax2)×V(λmax2))]≤+0.1,  (4)

{6} A white light source system configured to be capable of reproducingwhite light of a color temperature on a locus of blackbody radiation,and white light of a correlated color temperature with a deviation fromthe blackbody locus,

wherein an average color rendering index Ra of white light emitted fromthe white light source system is 95 or more, and all of color renderingindexes R₁ to R₈ and special color rendering indexes R₉ to R₁₅ are 85 ormore.

{7} The white light source system of {6}, wherein the white light sourcesystem is configured to be capable of reproducing white light of a colortemperature of 2000 K to 6500 K on the locus of the blackbody radiation,and white light of any one of correlated color temperatures with adeviation from the color temperature of the white light being in a rangeof ±0.005 duv.

{8} The white light source system of {7}, wherein the average colorrendering index Ra of the white light emitted from the white lightsource system is 97 or more, and all of the color rendering indexes R₁to R₈ and the special color rendering indexes R₉ to R₁₅ are 90 or more.

{9} The white light source system of any one of {6} to {8}, wherein P(λ), B(λ) and V(λ) satisfy an equation (1) below in a wavelength range inwhich λ is 380 nm to 780 nm, and the P(λ) and the B(λ) satisfy anexpression (2) below in a wavelength range of 400 nm to 495 nm:

$\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1) \\{{{P(\lambda)}/{B(\lambda)}} \leq {1.8.}} & (2)\end{matrix}$

where P(λ) is a light emission spectrum of white light emitted from thewhite light source system, B(λ) is a light emission spectrum ofblackbody radiation of a color temperature correspond to a colortemperature of the white light source system, and V(λ) is a spectrum ofa spectral luminous efficiency.

{10} A white light source system configured to be capable of reproducingwhite light of a color temperature on a locus of blackbody radiation,and white light of any one of correlated color temperatures with adeviation from the color temperature of the white light being in a rangeof ±0.005 duv,

-   -   wherein the white light source system includes LED modules        configured to emit white light of at least two chromaticity        points on an xy chromaticity diagram having a plus deviation on        a blackbody locus and white light of at least two chromaticity        points on the xy chromaticity diagram having a minus deviation        on the blackbody locus, and a controller configured to control        light emission intensities of the LED modules, the white light        source system being configured to be capable of obtaining white        light by mixing emission lights from at least four kinds of LED        modules controlled to have arbitrary intensities.

{11} A white light source system configured to be capable of reproducingwhite light of a color temperature of 2000 K to 6500 K on a locus ofblackbody radiation, and white light of any one of correlated colortemperatures with a deviation from the color temperature of the whitelight being in a range of ±0.005 duv,

wherein the white light source system includes LED modules configured toemit white light of at least three chromaticity points on an xychromaticity diagram having a plus deviation on a blackbody locus andwhite light of at least three chromaticity points on the xy chromaticitydiagram having a minus deviation on the blackbody locus, and acontroller configured to control light emission intensities of the LEDmodules, the white light source system being configured to be capable ofobtaining white light by mixing emission lights from at least six kindsof LED modules controlled to have arbitrary intensities.

{12} The white light source system of {10} or {11}, wherein P(λ), B(λ)and V(λ) satisfy an equation (1) below in a wavelength range in which λis 380 nm to 780 nm, and the P(λ) and the B(λ) satisfy an expression (2)below in a wavelength range of 400 nm to 495 nm:

$\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1) \\{{{P(\lambda)}/{B(\lambda)}} \leq {1.8.}} & (2)\end{matrix}$

where P(λ) is a light emission spectrum of white light emitted from thewhite light source system, B(λ) is a light emission spectrum ofblackbody radiation of a color temperature correspond to a colortemperature of the white light source system, and V(λ) is a spectrum ofa spectral luminous efficiency.

{13} The white light source system of any one of {10} to {12}, whereinthe LED module includes an LED configured to emit primary light ofultraviolet to violet with a light emission peak wavelength of 360 nm to420 nm, and a phosphor configured to absorb the primary light from theLED and to emit secondary light of white.

{14} The white light source system of {13}, which includes a phosphorlayer including the phosphor and a resin.

{15} The white light source system of {14}, wherein the phosphor layercovers the LED, and an intensity of LED primary light emitted from thewhite light source is 0.4 mW/lm (lumen) or less.

{16} The white light source system of {15}, which includes a powdermaterial layer and a thin film,

wherein the powder material layer includes a resin material and at leastone kind of powder material selected from among zinc oxide, titaniumoxide and aluminum oxide, and is formed on an outside of the phosphorlayer, the thin film includes at least one kind selected from among thezinc oxide, titanium oxide and aluminum oxide, and is formed on atransparent member which constitutes a cover of the white light sourcesystem.

{17} The white light source system of {15} or {16}, which includes apowder material layer and a thin film,

wherein the powder material layer includes a resin material and at leastone kind of powder material selected from among silicon oxide andzirconium oxide, and formed on an outside of the phosphor layer, and thepowder material layer includes at least one kind selected from betweenthe silicon oxide and the zirconium oxide, and is formed on atransparent member which constitutes a cover of the white light sourcesystem.

{18} The white light source system of any one of {13} to {17}, whereinthe phosphor is a mixture of at least four kinds selected from the groupconsisting of a blue phosphor, a green phosphor, a yellow phosphor and ared phosphor.

{19} The white light source system of {18}, wherein a blue-greenphosphor is further contained in the phosphor mixture.

{20} The white light source system of {18}, wherein the blue phosphor isat least one kind selected from between a europium activated strontiumaluminate phosphor having a light emission peak wavelength of 480 to 500nm, and a europium activated alkaline earth phosphate phosphor having alight emission peak wavelength of 440 to 460 nm.

{21} The white light source system of any one of {18} to {20}, whereinthe green phosphor is at least one kind selected from among a europiumactivated orthosilicate phosphor having a light emission peak wavelengthof 520 to 550 nm, a europium activated β-sialon phosphor having a lightemission peak wavelength of 535 to 545 nm, and a europium activatedstrontium sialon phosphor having a light emission peak wavelength of 520to 540 nm.

{22} The white light source system of any one of {18} to {21}, whereinthe yellow phosphor is a europium activated orthosilicate phosphorhaving a light emission peak wavelength of 550 to 580 nm, or a ceriumactivated rare earth aluminum garnet phosphor having a light emissionpeak wavelength of 550 to 580 nm.

{23} The white light source system of any one of {18} to {22}, whereinthe red phosphor is at least one kind selected from among a europiumactivated strontium sialon phosphor having a light emission peakwavelength of 600 to 630 nm, a europium activated calciumnitridoaluminosilicate phosphor having a light emission peak wavelengthof 620 to 660 nm, a europium activated lanthanum oxysulfide phosphorhaving a light emission peak wavelength of 620 to 630 nm, and amanganese activated magnesium fluorogermanate phosphor having a lightemission peak wavelength of 640 to 660 nm.

{24} The white light source system of any one of {1} to {5}, wherein theP(λ) and the B(λ) satisfy an expression (5) below in the wavelengthrange of 400 nm to 495 nm:

P(λ)/B(λ)≤1.5.   (5)

{25} The white light source system of any one of {9} to {12}, whereinthe P(λ) and the B(λ) satisfy an expression (5) below in the wavelengthrange of 400 nm to 495 nm:

P(λ)/B(λ)≤1.5.   (5)

{26} The white light source system of any one of {1} to {25}, whereinsunlight, which varies in accordance with differences in latitude,longitude and inherent environment in an arbitrary place on the earth,is reproduced as white light having a correlated color temperature, andthe correlated color temperature, which varies from time to time, issuccessively reproduced.

{27} The white light source system of {26}, further including a databasestoring spectra of sunlight varying in accordance with variations withtime in major regions at home and abroad,

wherein light emission intensities of the plural of LED modules arecontrolled based on desired sunlight spectrum data in the database, andsunlight corresponding to an arbitrary time of year in an arbitraryregion can be reproduced.

{28} The white light source system of any one of {1} to {27}, whereinthe white light source system is used as illumination for an office or ahome.

{29} The white light source system of any one of {1} to {27}, whereinthe white light source system is used as illumination for a work of artand craft exhibited in an art museum, a museum or the like.

A white light source system configured to be capable of reproducingwhite light of an arbitrary color temperature on a locus of blackbodyradiation, and white light of a correlated color temperature with anarbitrary deviation from the locus of the blackbody radiation,

wherein P(λ), B(λ) and V(λ) satisfy an equation (1) below in awavelength range in which λ is 380 nm to 780 nm, the P(λ) and the B(λ)satisfy an expression (2) below in a wavelength range of 400 nm to 495nm:

$\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1) \\{{{P(\lambda)}/{B(\lambda)}} \leq {1.8.}} & (2)\end{matrix}$

where P(λ) is a light emission spectrum of white light emitted from thewhite light source system, B(λ) is a light emission spectrum ofblackbody radiation of a color temperature correspond to a colortemperature of the white light source system, and V(λ) is a spectrum ofa spectral luminous efficiency.

A white light source system configured to be capable of reproducingwhite light of a color temperature on a locus of blackbody radiation,and white light of a correlated color temperature with a deviation fromthe locus of the blackbody radiation,

wherein an average color rendering index Ra of white light emitted fromthe white light source system is 95 or more, and all of color renderingindexes R₁ to R₈ and special color rendering indexes R₉ to R₁₅ are 85 ormore.

The white light source of the present invention can reproduce a spectrumshape of blackbody radiation, and can also approximate a light emissionspectrum having the same shape as sunlight reaching the earth, by takinginto account a difference in time and a difference in region. Thus, ifthe white light source is utilized for illumination in an art museumwhere articles on exhibition, such as works of art, are displayed, it ispossible to obtain the illumination which can be made close to the samesunlight as in the time and place in which the articles on exhibitionwere created, and can more accurately reproduce the creator's intention.

In addition, the white light source of this invention can successivelyreproduce variations of sunlight in a day, that is, color temperaturevariations of sunlight which is changing every moment from sunrise tosunset. Thus, when the white light source is used as illumination forworks of art, etc., it is possible to enjoy, while staying in the artmuseum, the colors of paintings which are irradiated with varioussunlights ranging from morning sunlight to evening sunlight, withnatural variations of the colors. Besides, when the white light sourceis used as illumination in a hospital or the like, it is possible tosense, while staying in the hospital, sunlight all day, even includingcolor temperature variations. In particular, since the state of changingis reproduced as a minute difference which is imperceptible to humans,an inpatient, for example, is unable to perceive a moment when the colortemperature varies, and thus the illumination is very natural andacceptable to the inpatient. In addition, in this white light source,compared to conventional artificial white light sources, the intensityof a blue emission light component, etc. is greatly reduced, and,needless to say, the illumination is kind to human bodies, etc.

(Light Emission Characteristics of White Light Source)

A white light source of the present invention aims at more accuratelyreproducing light of the sun. In order to achieve accurate reproduction,it is necessary to exactly grasp light emission spectra of sunlightwhich varies from time to time, and varies from place to place. Of suchvariations, a variation due to a difference in latitude or longitude ofthe earth occurs because the distance of passage of sunlight travelingthrough the atmosphere on the surface of the earth varies depending onthe difference of the incidence angle of the sunlight. Specifically,when sunlight passes through the atmospheric air, the sunlight isscattered by gas molecules, etc. floating in the air, and a differenceoccurs in the degree of scattering of blue light or the like due to thedistance of passage. Such a variation of sunlight can be macroscopicallygrasped as a difference in color temperature. In this case, lightemission spectra of sunlights with different color temperatures can beapproximated by blackbody radiation spectra of the corresponding colortemperatures. By the equation described below, various light emissionspectra with different color temperatures can relatively easily bereproduced. In the equation, h denotes a Planck's constant, k denotes aBoltzmann's constant, c denotes the speed of light, and e denotes a baseof natural logarithm, and these values are fixed at constant numericalvalues. Thus, if a color temperature T is determined, a spectraldistribution B(λ) corresponding to each wavelength λ can easily becalculated.

$\begin{matrix}{{B(\lambda)} = {\frac{2{hc}^{2}}{\lambda^{5}} \cdot \frac{1}{e^{{{hc}/\lambda}\;{kT}} - 1}}} & (6)\end{matrix}$

On the other hand, the light emission spectrum of sunlight varies, notonly simply depending on the latitude and longitude, but also dependingon regional differences. In this case, various factors of variations arethinkable. To begin with, as regards the influence of light scattering,the scattering relates to not only molecules of air and gas, but alsofine particles such as moisture vapor, dust, etc. However, for example,the density of moisture vapor, dust, etc. varies from region to region.As a matter of course, there are large differences between a region nearthe sea and a region near the desert. Furthermore, the influence ofreflection, as well as scattering, is not negligible. Specifically, thelight, which humans perceive as sunlight, includes not only direct lightfalling from the sun, but also light which is reflected after reachingthe earth. It is natural that there are differences of light componentsincluded in the reflected light between a region near the sea, a regionnear a forest, and a densely built-up urban area. In this manner, thevariations of sunlight due to regional differences are a complex mixtureof many factors, and there is no general regularity. It is necessary tounderstand that the variations of sunlight due to regional differencesare based on factors inherent to regions.

In the present invention, in order to reproduce such variations ofsunlight, the light emission spectra of sunlight, which vary from regionto region and from time to time, are actually measured, and as much aspossible data is collected, stored and utilized. Thereby, the variationsof sunlight are reproduced. Concretely, the light emission spectra ofsunlight are measured in major regions around the world, and one-dayvariations from hour to hour, and yearly variations from season toseason are accumulated as data. In the present invention, theaccumulated data, in principle, relates to clear days, and noconsideration is given to the influences of clouds, rain, snow, etc.

FIG. 1 shows an example of a light emission spectrum of sunlight in thedaytime (12:00 p.m.) in winter (December 16) in Milan, Italy. FIG. 2shows an example of a light emission spectrum of sunlight in the evening(17:00 p.m.) in spring (May 27) in Tokyo. These light emission spectrawere measured by the following method.

A light detection portion of a colorimetry device (spectral distributionmeasuring device), in which a diffraction grating is incorporated andhas a wavelength component resolving function of light intensity, wasdirected to the sun. Sunlight was directly taken in the spectraldistribution measuring device, and light emission spectra were measured.The wavelength range for measurement was set to 360 nm to 780 nm, whichcovers the visible light range. As regards the adjustment of lightintensity that is taken in the spectral distribution measuring device,by an exposure time adjustment function which is incorporated in themeasuring device, it was confirmed that no saturation phenomenonoccurred even in a wavelength region with high light emission intensity.As regards the measurement result, light intensity for each wavelengthwas calculated from electronic data. Based on this result, CIEchromaticity coordinate values, correlated color temperatures anddeviations were calculated. CIE is the acronym of the CommissionInternationale de l'Eclairage.

Each of the light emission spectra is formed of an irregular curve. Ifthe curves are smoothed, the curves can be approximated to the shape ofa blackbody radiation spectrum of an arbitrary color temperature. If thetwo Figures are compared, since the positions of irregularities in thespectrum curves overlap, it is understood that the irregularities arebased not on noise or the like, but on factors inherent to specificfloating matter, etc. In particular, portions indicative ofcharacteristic irregularities are present in long wavelength regions,and the degree of irregularities is large. It is thus presumed that thespectrum shape of these wavelength regions is one of factors which causeregional differences or the like. If light emission colors arecalculated based on the spectral shapes of FIG. 1 and FIG. 2, it turnedout that the light in FIG. 1 is white light indicative of a correlatedcolor temperature of 5991 K+0.001 duv, and the light in FIG. 2 is whitelight indicative of a correlated color temperature of 4483 K−0.001 duv.

The comparison between only two places was described above. However,when the spectral data of sunlight in respective regions and atrespective times were compared and evaluated, and the tendency as awhole was confirmed, it turned out that, as a matter of course, thelight emission color indicates a point close to a blackbody locus on the(x, y) chromaticity diagram. Moreover, it turned out that the lightemission color does not always completely agree with the point on theblackbody locus, and that almost all data fall within the range ofcorrelated color temperatures with a deviation of ±0.005 duv on ablackbody locus having color temperatures of from 2000 K to 6500 K.

In the white light source of the present invention, all light emissioncolors in the above range can be reproduced. Concretely, for example, asshown in FIG. 3, light emission colors in a range surrounded by x1, x2,x3, x4, x5 and x6 in the Figure can be reproduced. Thus, the white lightsource of the present invention includes six kinds of white lightsources corresponding to x1, x2, x3, x4, x5 and x6. Specifically, bymixing at least two or more of the six kinds of white light sources withany intensities, all light emission colors in the polygonal range can bereproduced. From FIG. 3, it is understood that the range of this shapecovers all the light emission colors on the blackbody locus from 2000 Kto 6500 K of color temperatures and the white light region with thedeviation from the blackbody locus in the range of ±0.005 duv.Accordingly, in the white light source of the present invention, it ispossible to reproduce not merely white light on the blackbody locus, butalso subtle deviations of color temperatures which vary due to variousenvironmental factors on the earth.

The color reproduction in the range of the specific polygon or the likewas described above. However, needless to say, various white lights canbe reproduced by setting light emission colors corresponding to therespective vertices of the polygon as white lights of various correlatedcolor temperatures. In addition, in the above-described white lightsource, six kinds of white light sources were arbitrarily mixed, and thewhite light emission of the invention was obtained. However, needless tosay, sunlights of various color temperatures can be reproduced morefinely, by utilizing a greater number of kinds of basic white lightsources, for example, eight kinds or ten kinds of white light sources.In particular, this is advantageous when white lights of a wider rangeof color temperatures are reproduced by a single white light sourcesystem. However, if the number of kinds of basic light sources isexcessively large, the design of the system becomes complex. If at leastfour kinds of light sources are used, the advantageous effects of thepresent invention can, at least, be exhibited. Besides, the range ofcolor temperatures of white light to be reproduced is 2000 K to 6500 K.By setting these values as the upper and lower limits, colortemperatures between two or more kinds of arbitrary light sources can beselected as the range of reproduction.

Furthermore, in the white light source system of the present invention,not only the light emission colors of sunlight, but also the lightemission spectra can be reproduced. In the white light source systemincluding at least four kinds of white light sources, such as theabove-described x1 to x6, each white light source includes all lightemission components which can reproduce the light emission spectra ofsunlight. Accordingly, when at least two or more kinds of white lightsources of the above-described four or more kinds of white light sourcesare combined, and white light of any color temperature on the blackbodylocus or white light of any correlated color temperature close to theblackbody locus is reproduced, the light emission spectral shape of themixed white light will be similar to the light emission spectral shapeof the blackbody radiation of the corresponding color temperatures.

Concretely, a light emission spectrum of a white light source of thepresent invention is characterized by satisfying the followingexpression (3):

−0.2≤[(P(λ)×V(λ))/(P(λmax1)×V(λmax1))−(B(λ)×V(λ))/(B(λmax2)×V(λmax2))]≤+0.2,  (3)

where P(λ) is the light emission spectrum of mixed white light emittedfrom the white light source system; B(λ) is the light emission spectrumof blackbody radiation having the same color temperature as that of thewhite light source; V(λ) is the spectrum of a spectral luminousefficiency; λmax1 is the wavelength at which P(λ)×V(λ) is largest; andλmax2 is the wavelength at which B(λ)×V(λ) is largest.

The (P(λ)×V(λ)) indicates the intensity of the light emission spectrumof the white light source in a spectral luminous efficiency V(λ) region.The (P(λ)×V(λ)) is divided by (P(λmax1)×V(λmax1)) that is the maximumvalue, whereby the upper limit thereof can be 1.0. Further, the(B(λ)×V(λ)) indicates the intensity of the light emission spectrum ofthe blackbody radiation in the spectral luminous efficiency V(λ) region.The (B(λ)×V(λ)) is divided by (B(λmax2)×V(λmax2)) that is the maximumvalue, whereby the upper limit thereof can be 1.0. Next, a differenceA(λ)=[(P(λ)×V(λ))/(P(λmax1)×V(λmax1))-(B(λ)×V(λ))/(B(λmax2)×V(λmax2))]is obtained. If the difference A(λ) is −0.25≤A(λ)≤+0.2, the lightemission spectrum of the white light source in the spectral luminousefficiency V(λ) region is close to the light emission spectrum of theblackbody radiation, that is, the light emission spectrum of naturallight. Specifically, if the difference A(λ) is A(λ)=0, the same lightemission spectrum as that of the natural light can be reproduced.

Furthermore, in order to more precisely reproduce the light emissionspectrum of blackbody radiation, it is preferable that the white lightsource of the present invention satisfies the following expression (4):

−0.1≤[(P(λ)×V(λ))/(P(λmax1)×V(λmax1))−(B(λ)×V(λ))/(B(λmax2)×V(λmax2))]≤+0.1,  (4)

In this manner, in the white light source system of the presentinvention, at least four kinds of basic white light sources include,without excess or deficiency, the respective light emission colorcomponents which sunlight has, and each white light, in which the atleast four kinds of light sources are mixed at an arbitrary ratio, alsoincludes the light emission components which sunlight has. In otherwords, the white light obtained by the white light source system of thepresent invention has the characteristics of the blackbody radiationspectrum of each color temperature, and can reproduce fine variations ofany wavelength regions.

In addition, in the white light source system of the present invention,one-day variations of sunlight can be expressed as successive variationswhich are very natural to human eyes. According to the result whichDavid Lewis MacAdam derived from isochromatic experiments of the senseof sight (“Shikisai Kougaku” [Color Engineering], 2nd ed., Tokyo DenkiUniversity Press), it was found that if the standard deviation ofdiscernment variations for a central color is expressed on the xychromaticity diagram, this standard deviation is expressed in a range ofa shape called “MacAdam ellipse”, and the range of color temperatureswhich humans can discern is three times the standard deviation.According to this finding, if calculation is made with respect to whitelight of 5000 K, the value of 330 K (from 4850 K to 5180 K) was obtainedas the threshold of discernment. Thus, for example, in the case of whitelight of 5000 K, a difference between color temperatures of about 330 Kor less cannot be discerned by human eyes.

FIG. 4 is a graph showing a color temperature variation and anilluminance variation of sunlight from 6:00 a.m. to 6:00 p.m. in a dayin spring in Tokyo at latitude 35° N. In FIG. 4, a graph denoted byreference sign 1 indicates the color temperature variation, and a graphdenoted by reference sign 2 indicates the illuminance variation. Thegraphs were created based on the result of actual measurement for everythree minutes of the variation with time of sunlight. In the Figure, theilluminance is expressed as an illuminance ratio (%) by relativecomparison to a certain value as a reference. In addition, since theone-day color temperature variation of sunlight is a rate ofapproximately a little less than 200 K per three minutes, the differencein color temperature in every measurement unit in the invention is notperceivable to human eyes. Accordingly, even when the color temperaturevariation is reproduced by using the measurement data, the moment atwhich the color temperature of the light source changes cannot berecognized, and the variation can be accepted in a natural manner, as ifthe color temperature varied continuously.

(LED Module)

The feature of the white light source of the present invention is in thelight emission characteristics. The white light source may employ anystructural member as long as the white light source can reproducesunlight. Thus, various light sources are applicable. In order to obtainwhite lights of various color temperatures, the simplest method is amethod of adjusting light emission colors by using phosphors, thus aphosphor-applied product is desirable. In particular, a light sourcecreated by combining an LED (light-emitting diode) with phosphor hasexcellent features, not only in characteristics but also in manufactureand application, and is optimal. In this case, in order to obtain whitelight, any combinations of various light emission colors of LEDs andvarious light emission colors of phosphors can be selected.

On the other hand, in order to obtain further preferable white light, itis preferable to use a peak wavelength in a range of an ultraviolet toviolet region, to be more specific, a range of 360 to 420 nm. When anLED having a light emission peak wavelength in a range exceeding 420 nmis produced, the LED exhibits a sharp light emission at a specificwavelength. Consequently, the balance between this light emission andthe light emission of a phosphor having a generally broad spectral shapebecomes poorer, and it may be difficult to satisfy the relations of theabove expressions (3) and (4). However, if the light emission color ofthe LED is in a range of ultraviolet to violet, since the luminosityfunction is low, the influence on white light is small. In addition, theprimary light is not emitted from the light emission device by cuttingout the primary light from the LED. Therefore, it becomes easy tosatisfy the relations of the above expressions.

In order for the light emission spectrum of the white light source tosatisfy the relations of the above expressions (3) and (4), it ispreferable to use three or more, or, more preferably, five or more, fromamong a blue phosphor, a blue-green phosphor, a green phosphor, a yellowphosphor, and a red phosphor, as phosphors to be combined in the LED. Byarbitrarily mixing these phosphors in accordance with a correspondingblackbody radiation spectrum, white light emission having an arbitrarycolor temperature or an arbitrary deviation can be obtained. It ispreferable to use a phosphor which is excited by an LED having a lightemission peak wavelength of 350 to 420 nm, and exhibits a light emissionpeak in a range of 420 to 700 nm. In addition, it is preferable that thepeak wavelengths of the respective phosphors deviate by 150 nm or less,or more preferably, by 10 to 100 nm, or still more preferably, by 10 to50 nm. In other words, it is preferable that the distance between acertain peak wavelength and a neighboring peak wavelength is 150 nm orless, or more preferably 10 to 100 nm, or still more preferably 10 to 50nm. It is preferable that the light emission spectra of at least twokinds of phosphors constituting the mixture of phosphors satisfy thisrelationship. In addition, the half-value width of the light emissionspectrum of at least one kind of phosphor constituting the mixture ofphosphors is as wide as 50 nm or more, and more preferably 50 to 100 nm.By using the phosphors which satisfy these conditions, the lightemission spectrum of each phosphor tends to more easily overlap thelight emission spectra of other phosphors. The larger the overlappingarea between the light emission spectra, the easier it is to obtain thecharacteristics of a spectral curve of the obtained mixed white light,and the spectral curve will show less irregularity, be smoother, and becloser to the spectrum of blackbody radiation.

Besides, by using plural phosphors with overlapping light emissionspectra, it is possible to suppress a variation in light emission colorupon long-time continuous lighting. Among the phosphors used in thepresent invention, there exists a phosphor having a wide absorptionband. Such a phosphor can be not only excited by ultraviolet or violetlight, but can also be simultaneously excited by blue light or greenlight and can emit green light or red light. If a plural of suchphosphors with overlapping light emission spectra are used,re-absorption or double excitation tends to more easily occur, whichmeans that it is easier to suppress any variation in light emissioncolor. For example, a green phosphor is not only excited by ultravioletor violet light emitted from the LED and emits green light, but also thegreen phosphor absorbs light of a blue phosphor which is excited by theLED and emits blue light, and can emit green light. Specifically, thegreen phosphor can emit light by double excitation by the LED and bluephosphor. In general, in an artificial white light source, white lightis obtained by mixing, within the device, emission lights of a plural ofphosphors such as red, green and blue phosphors. When this white lightsource is continuously turned on, the brightness of phosphors, in usualcases, gradually decreases with time. Therefore, if the brightnesses ofthe respective phosphors equally vary with time, the chromaticity of theobtained white light is unchanged. However, of a plural of kinds ofphosphors, if the luminance degradation rate of a certain kind ofphosphor is different from the luminance degradation rates of some otherphosphors, excess or deficiency of light emission of a certain componentoccurs in the obtained white light, and a change occurs in the obtainedlight emission color. However, if mutual absorption or double excitationoccurs as in the present invention, the degradation rates are averagedbetween the phosphors, and it is possible to suppress degradation ofonly a certain phosphor. As a result, the chromaticity variation of theobtained white light decreases.

In the meantime, as regards a phosphor, what wavelength causesexcitation of the phosphor and what wavelength causes light emission ofthe phosphor can easily be confirmed by measuring the excitationspectrum or light emission spectrum of the phosphor. Accordingly, iflight emission spectrum characteristics are measured in advance and thena combination of phosphors to be used is selected, the chromaticityvariation during continuous lighting can be reduced as much as possible.By utilizing the above advantageous effects, the white light sourcesystem of the present invention can reduce the magnitude of thechromaticity variation between the initial time of lighting of the whitelight source and the time after continuous lighting of 6000 hours to0.010 or less with use of the CIE chromaticity diagram. In the method ofmeasuring the magnitude of the chromaticity variation, chromaticitycoordinates u′ and v′ at the initial time of lighting of the white lightsource and at the time after continuous lighting of 6000 hours aremeasured, respectively, according to JIS-Z-8518. Differences Δu′ and Δv′between the chromaticity coordinates at this time are calculated, andthe magnitude of the chromaticity variation =[(Δu′)²+(Δv′)²]^(1/2) iscalculated. In the white light source system of the present invention,the magnitude of this chromaticity variation can be decreased to assmall as less than 0.010, and, furthermore, to less than 0.009. That themagnitude of chromaticity variation is less than 0.010 refers to thestate in which there is no substantial change of color from the initialtime of lighting even in the case of long-time use. Thus, sunlight canbe reproduced for a long time.

Concrete phosphors, which are usable in the white light source system ofthe present invention, are as follows. Examples of the blue phosphorinclude a europium activated alkaline earth phosphate phosphor (a peakwavelength of 440 to 455 nm), and a europium activated barium magnesiumaluminate phosphor (a peak wavelength of 450 to 460 nm). Further,examples of the blue-green phosphor include a europium activatedstrontium aluminate phosphor (a peak wavelength of 480 to 500 nm), and aeuropium and manganese activated barium magnesium aluminate phosphor (apeak wavelength of 510 to 520 nm). Examples of the green phosphorinclude a europium activated orthosilicate phosphor (a peak wavelengthof 520 to 550 nm), a europium activated (3-sialon phosphor (a peakwavelength of 535 to 545 nm), and a europium activated strontium sialonphosphor (a peak wavelength of 520 to 540 nm). Examples of the yellowphosphor include a europium activated orthosilicate phosphor (a peakwavelength of 550 to 580 nm), and a cerium activated rare earth aluminumgarnet phosphor (a peak wavelength of 550 to 580 nm). Examples of thered phosphor include a europium activated strontium sialon phosphor (apeak wavelength of 600 to 630 nm), a europium activated calciumnitridoaluminosilicate phosphor (a peak wavelength of 620 to 660 nm), aeuropium activated lanthanum oxysulfide phosphor (a peak wavelength of620 to 630 nm), and a manganese activated magnesium fluorogermanatephosphor (a peak wavelength of 640 to 660 nm).

FIG. 34 shows a light emission characteristic of the europium activatedorthosilicate phosphor of green light emission, and shows a lightemission spectrum 57 having a peak at 527 nm, and an excitation spectrum58 corresponding to light emission of the peak wavelength 527 nm. As isunderstood from FIG. 34, a long wavelength end of the excitationspectrum 58 of this phosphor spreads to approximately 525 nm, and thephosphor is excited by ultraviolet light, violet light, blue light orblue-green light, and exhibits green light emission. Similarly, FIG. 35shows a light emission spectrum 59 and an excitation spectrum 60 of theeuropium activated calcium nitridoaluminosilicate phosphor of red lightemission. The excitation spectrum 60 of this phosphor spreads from anultraviolet region to yellow region, and it is understood that thephosphor is excited by ultraviolet light, violet light, blue light orgreen light, and also by yellow light, and exhibits red light emission.When a light source of white light emission is constituted by combiningthe above two kinds of phosphors with a violet LED and a blue phosphor,the blue phosphor is excited by the LED, the green phosphor is excitedby the LED and blue phosphor, the red phosphor is excited by the LED,blue phosphor and green phosphor, and re-absorption and multipleexcitation occur between the phosphors. In this light source, even if alarge luminance degradation occurs in the blue phosphor due to avariation with time, the luminance variation of blue light also affectsthe luminance of the green phosphor and red phosphor, and the luminancevariation as a whole is averaged. As a result, the suppression effect ofchromaticity variation of white light can be obtained.

Table 1-1 is a list of half-value widths with respect to light emissionspectra of phosphors used in the present invention. The numerical valuesin the Table show, as representative values, the half-value widths oflight emission spectra corresponding to main peaks, with respect to thelight emission spectra of the respective phosphors. As is understoodfrom Table 1-1, although there are some exceptions, the half-valuewidths of most of the phosphors are 50 nm or more. If phosphors to beused are properly selected, it is possible to constitute a white lightsource in which all phosphors with half-value widths of 50 nm or moreare combined.

TABLE 1-1 Light Half-width emission values colors Phosphor compounds(nm) Blue europium activated alkaline earth phosphate 50 phosphor Blueeuropium activated barium magnesium aluminate 55 phosphor Blue-greeneuropium activated strontium aluminate phosphor 61 Blue-green europiumand manganese activated barium 12 magnesium aluminate phosphor Greeneuropium activated orthosilicate phosphor 65 Green europium activatedβ-sialon phosphor 58 Green europium activated strontium sialon phosphor60 Yellow europium activated orthosilicate phosphor 89 Yellow ceriumactivated rare earth aluminum garnet 75 phosphor Red europium activatedstrontium sialon phosphor 110 Red europium activated calciumnitridoaluminosilicate 93 phosphor Red europium activated lanthanumoxysulfide 15 phosphor Red manganese activated magnesium fluorogermanate33

A phosphor is mixed with a resin material, and is used in the form of aphosphor film (phosphor layer). The periphery of the LED chip isdirectly or indirectly covered with the phosphor layer. Thereby, primarylight, which is emitted from the LED, is converted to secondary light(white light) by the phosphor layer, and the secondary light is radiatedto the outside.

(Light Emission Characteristics of LED Module)

By using the above-described combination of the LED and phosphors, thewhite light source of the present invention can exhibit a light emissionspectral distribution which is substantially equal to the light emissionspectral distribution of sunlight. Accordingly, when the white lightsource of the present invention is used for illumination, high colorrendering properties, which are equal to those of sunlight, can beexhibited, and an average color rendering index Ra can be set to 95 ormore. Moreover, not only the mean value, but also all of the colorrendering indexes R₁ to R₈ and special color rendering indexes R₉ to R₁₅can be set to 85 or more.

Furthermore, according to a more preferable white light source of thepresent invention, it is possible to set the average color renderingindex Ra to 97 or more, and set all of the color rendering indexes R₁ toR₈ and special color rendering indexes R₉ to R₁₅ to 90 or more.

Besides, when the white light source of the present invention isutilized not as illumination for inorganic objects such as works of art,but as illumination for human bodies, it is possible to realizeillumination which is kind to human bodies as if it were sunlight. Alongwith the recent popularity of LED illumination, attention has been paidto the problems of blue light hazards. In regard to such problems, thereis a concern over the various hazards to human bodies. For example,since the intensity of a blue light component included in the whiteemission light is excessively high, use over a long time leads to eyefatigue. Moreover, excessive exposure to LED white light at night leadsto a disturbance of the human circadian rhythm. As regards conventionalLED white light, white light is obtained by combining a blue LED with ayellow phosphor or the like, and this is considered to be a factorrelated to the above hazards. A phosphor generally exhibits a broadlight emission spectrum, while a blue LED has an excessively sharpspectrum shape having a peak at a specific blue wavelength. Thus, ifboth are combined, only an unnatural white light emission spectraldistribution with a spike of a blue wavelength region can be obtained.On the other hand, as described above, the light emission spectraldistribution of the white light source of the present invention does nothave an unnatural spike portion in the blue wavelength region, and thelight emission spectrum of sunlight, including the blue wavelengthregion, can be reproduced. Therefore, the white light source of thepresent invention can be utilized as an illumination light source kindto human bodies, which does not cause blue light hazards, etc.

Even if blue light has a possibility of being harmful to human bodies, ablue component of a fixed intensity needs to be included in white light,in order to obtain white illumination of high color rendering. If theobject is to merely obtain white light with a small blue component, itshould suffice to select a white light source with a low colortemperature. The reason for this is that as the color temperaturebecomes lower, a relative content of a red component or the likeincluded in the white light increases and a relative content of bluelight or the like decreases. However, the object of the white lightsource of the present invention is to reproduce sunlight of all colortemperatures. Accordingly, such reproduction cannot be restricted toonly reproduction of a specific color temperature in consideration ofthe hazardous property to human bodies. Thus, in the present invention,a P(λ)/B(λ) value, which will be described below, is adopted as an indexwhich characterizes the properties of the white light source of thepresent invention, the P(λ)/B(λ) value serving as the criterion forsatisfying, at the same time, both the color rendering property for thepurpose of use as illumination and the safety to human bodies.

Assuming that the light emission spectrum of the white light source ofthe present invention is P(λ), the light emission spectrum of blackbodyradiation of the corresponding correlated color temperature is B(λ), andthe spectrum of the spectral luminous efficiency is V(λ), when thesesatisfy the following equation (1),

$\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1)\end{matrix}$

the light emission spectrum of the white light source of the inventioncan satisfy, in a wavelength range of 400 nm to 495 nm, a relationalexpression:

P(λ)/B(λ)≤1.8   (2)

Accordingly, in the wavelength range of 400 nm to 495 nm, even if thereis a wavelength region in which the intensity of P(λ) exceeds theintensity of B(λ), the intensity ratio ((P(λ)/B(λ)) between both in thiswavelength region never exceeds 1.8 at maximum. Incidentally, in a morepreferable white light source of the present invention, when P(λ)V(λ)and B(λ)V(λ) satisfy the above equation, a relational expression (5):

P(λ)/B(λ)≤1.5   (5)

can be satisfied in the wavelength range of 400 nm to 495 nm.Accordingly, the white light source of the present invention exhibits agentler, smoother, continuous spectrum, without an excessive spike oflight emission intensity at a specific wavelength in the blue wavelengthregion.

The lower limit value of the above-described P(λ)/B(λ) value is notparticularly limited. When sunlight is reproduced, it is preferable thatthe P(λ)/B(λ) value indicates a value close to 1. The reason for this isthat if light of wavelengths of 495 nm or less is deficient, the colorof an illumination target cannot be reproduced as a natural color.However, as described above, the white light source of this invention isa light source which can exhibit fixed values or more of the averagecolor rendering index and special color rendering indexes. In addition,as indicated by the above expressions (3) and (4), the white lightsource of this invention has the feature that approximation is made tothe light emission spectrum of blackbody radiation over the entirevisible light wavelength range. Accordingly, even if the lower limitvalue of the P(λ)/B(λ) value is not particularly set, the substantialcharacteristics required for the white light source of the presentinvention are satisfied. The P(λ)/B(λ) value of the white light sourceindicates the ratio of a blue light component which is excessivelyincluded, compared to the light emission spectrum of blackbody radiationof the same color temperature. From the standpoint of the degree ofinfluence on human bodies, the upper limit value of the P(λ)/B(λ) valueis particularly important.

In the white light source of this invention, white light emission isobtained by the combination of phosphor light emissions. It ispreferable that as much energy of primary light as possible from the LEDis absorbed in the phosphor. At the same time, it is necessary toprevent LED light from leaking to the outside of the light source. Inparticular, when ultraviolet is included in the LED light, it ispossible that the body color of a work of art or the like is damaged, ora harmful effect is exerted on the skin or the like of the human body.Thus, the prevention of leakage is strongly required.

In the LED module of this invention, in order to prevent leakage ofultraviolet, a phosphor layer is formed to have a sufficient filmthickness. The phosphor layer is formed as a thick film, in order toprevent LED light, which is reflected by the surface of each phosphorparticle, from leaking to the outside of the light source through thephosphor layer. At this time, if the thickness of the phosphor layer istoo large, the emission light itself of the phosphor cannot exit fromthe phosphor layer, and the light emission intensity of the phosphorlayer lowers. It is generally known that the particle size of a phosphorand the optimal film thickness have a proportional relationship. In thephosphor layer of this invention, a phosphor, whose particles are aslarge as possible in practical use, is used, and the phosphor layer isformed as thick as possible. For this purpose, it is preferable that thephosphor used in the LED module of this invention has an averageparticle size in a range of 5 μm to 50 μm. A more preferable range ofthe average particle size is 10 μm to 40 μm. It is preferable that thethickness of the phosphor layer corresponding to this average particlesize is in a range of 0.07 mm to 1.5 mm. A more preferable range is 100μm to 1000 μm. In addition, it is preferable that the content of thephosphor in the phosphor layer is set such that the mass ratio of thephosphor in the phosphor layer is in a range of 60 mass % to 90 mass %.When the phosphor content is less than 60 mass %, there is concern thateven if the phosphor layer is made thick, the phosphor content in thephosphor layer becomes deficient. If the phosphor content is deficient,part of LED light passes through a gap between phosphor particles andleaks out of the white light source. On the other hand, if the phosphorcontent is too large, no problem arises with respect to the leakage ofLED light, but the amount of the binder, which binds phosphor particles,is too small, and a problem arises with respect to the physical strengthof the phosphor layer. In the above manner, an LED module can beobtained which suppresses leakage of ultraviolet to 0.4 mW/lm or less,and which avoids a reduction in light emission of the phosphor layer tothe extent possible.

In order to make it doubly sure to prevent ultraviolet leakage, anultraviolet absorption film may be formed on the outside of the phosphorlayer. In this case, as an ultraviolet absorption/reflection material,use can be made of fine particle white pigments such as zinc oxide,titanium oxide, aluminum oxide, etc. Like the phosphor layer, these fineparticle pigments are dispersed in a resin, and an ultravioletabsorption film is formed directly or indirectly on the outside of thephosphor layer. Thereby, the LED module of the objective can beobtained. In the thus obtained LED module of this invention, the amountof ultraviolet leaking to the outside of the module can be reduced to0.4 mW/lm or less.

The numerical value of the amount of ultraviolet can be calculated bythe following method. Assuming that the light emission spectrum of whitelight emitted from the light emission device is P(λ), and the spectrumof the spectral luminous efficiency is V(λ), both the P(λ) and the V(λ)are multiplied and integrated, and the following φ is calculated.

Φ=6 8 3·∫P(λ)·V(λ)dλ  (7)

In equation (7), 683 is a constant which satisfies 1 W=683 Lm at awavelength of 555 nm.

As regards primary light energy emitted from the LED, a spectrum F(λ) isintegrated in a range of 360 to 420 nm by the following equation, and UVbelow is calculated.

$\begin{matrix}{{UV} = {\int_{360}^{420}{{P(\lambda)}d\;\lambda}}} & (8)\end{matrix}$

The primary light energy per light flux, which is emitted from the lightemission device, can be calculated by UV/φ.

As described above, the white light source of the present invention hassubstantially the same light emission spectrum shape as that ofsunlight, and also has substantially the same intensity level of thelight emission spectrum in the wavelength region of blue light assunlight. When it is desired to more surely reduce the intensity of bluelight or violet light, or to make this intensity lower than the lightemission intensity of the blue component or violet component included inthe sunlight, a leakage prevention film for such light emissions may beformed. In this case, as absorption materials of violet light or bluelight, fine particle pigments of zirconium oxide or silicon oxide can beused. Like the phosphor layer, these fine particle pigments aredispersed in a resin, and an absorption film is formed directly orindirectly on the outside of the phosphor layer. Thereby, the LED moduleof the objective can be obtained. In addition, as a method having thesame advantageous effect as the above-described indirect method, ameasure may be taken by forming an evaporation deposition film ofzirconium oxide or silicon oxide on a transparent cover of a white lightsource, for example, a transparent globe member of an LED bulb.

(White Light Source System)

FIG. 27 illustrates an example of a white light source system of anembodiment. As illustrated in the Figure, the white light source systemof the embodiment includes a white light source unit 21 and a controller22. The white light source unit 21 includes a substrate 23, a plural ofwhite light sources 24 disposed on the substrate 23, and a lightemission device cover 25 which is fixed to the substrate 23 in a mannerto cover the plural white light sources. Each of the white light sources24 is composed of an LED module. The LED module includes an LED chip 26disposed on the substrate 23, and a phosphor layer 27 which is disposedon the substrate 23 and covers the LED chip 26. A wiring network isprovided on the substrate 23, and electrodes of the LED chips 26 areelectrically connected to the wiring network. In the meantime, the lightemission device cover 25 may be provided with a lens (not shown) whichis disposed on an outer surface of a wall portion facing the substrate23. Besides, at least a part of the light emission device cover 25 maybe formed as a transparent portion which can take out light. It ispreferable that the transparent portion is formed in a wall portion onthe side opposed to the substrate 23. Moreover, a reflector (not shown)can be disposed, for example, on an inner surface of the light emissiondevice cover 25.

The controller 22 includes a control unit 28, a memory unit 29, and adata input/output unit 30. The white light sources 24, which arecomposed of the LED modules, are connected to electronic circuit (notshown) of the control unit 28 by wiring lines 31. The white lightsources 24 emit light by being supplied with electric current flowingfrom the control unit 28 via the wiring lines 31. In the electroniccircuit memory unit 29 of the control unit 28, one-day variation data ofsunlight is stored with respect to each of places and each of seasons(times of year). In order to obtain an illumination light source of adesired pattern, a system user inputs place information, such as a cityname or latitude/longitude, and time information, such as a season, tothe data input/output unit 30. The obtained data is delivered to thecontrol unit 28. The control unit 28 extracts stored data correspondingto the input data, reads data of correlated color temperatures andilluminance of sunlight with respect to which the place and season werespecified, and calculates, based on these data, the mixture intensityratio of respective white light sources. Based on the calculationresult, the electronic circuit of the control unit 28 controls the valueof electric current which is applied to each white light source 24, andcan reproduce characteristic variations of required sunlight.

In the white light source system, the LED module including the LED andphosphor is used. The LED module includes a substrate, an LED chipdisposed on the substrate, and a phosphor layer formed in a manner tocover the periphery of the LED chip.

It is preferable that a material, such as alumina, aluminum nitride,silicon nitride or glass epoxy, is used for the substrate. Inparticular, it is more preferable to select an alumina substrate or aglass epoxy substrate, judging comprehensively from the standpoints ofheat conductivity, resistance to ultraviolet to violet light,insulation, reflectance, cost, etc. It is possible to use one kind ortwo or more kinds of materials which constitute the substrate.

As the material of the LED, any material may be used provided thematerial emits ultraviolet to violet light. For example, a GaN-basedmaterial, such as InGaN, GaN or AlGaN, can be used.

For example, as illustrated in FIG. 28, in an LED module 50, a greatnumber of LED chips 52 are arranged linearly on a substrate 51. Thenumber of chip lines may be one or more. A plural of chip lines can bearranged in accordance with the number of chips that are used. Forexample, in FIG. 28, a plural of chip lines are arranged in a matrix. Itis preferable that the LED chips 52 are arranged with a highest possibledensity. However, if the distances between the LED chips 52 are tooshort, mutual absorption of LED emission light occurs between the LEDchips 52, and this is undesirable. In addition, in order to promote theradiation of heat generated by the LED chips 52 at a time of continuouslighting, it is preferable to arrange the LED chips 52 at properintervals. In the meantime, the arrangement of the chips is not limitedto the linear arrangement. Also when the chips are arranged in astaggered fashion or the like, the arrangement with the same highdensity can be realized.

In FIG. 28, the respective LED chips 52 are connected by wires 53, andare connected to electrodes 54. The electrodes 54 have a pattern, andserve also as conductors on the substrate 51. It is preferable that atleast one kind of metal selected from among Ag, Pt, Ru, Pd, and Al isused as the material of the conductors. It is also preferable that an Aufilm is formed on the surface of the metal in order to prevent corrosionor the like. The Au film may be formed by using any one of a printingmethod, an evaporation deposition method and a plating method.

The periphery of the LED chip 52 on the substrate 51 is directly orindirectly covered with a phosphor layer. FIG. 29 to FIG. 33 illustrateexamples of disposition of the phosphor layer. As illustrated in FIG.29, a phosphor layer 55 may be directly formed on the surface of the LEDchip 52. As illustrated in FIG. 30, after the periphery of the LED chip52 is covered with the phosphor layer 55, the periphery of the phosphorlayer may be covered with a transparent resin layer 56. In addition, asillustrated in FIG. 31, after the surface of the LED chip 52 is coveredwith the transparent resin layer 56, a substantially entire surface ofthe transparent resin layer 56 may be covered with the phosphor layer55. In FIG. 29 to FIG. 31, a plural of LED chips 52 are covered with asingle phosphor layer 55 or transparent resin layer 56. Alternatively,as illustrated in FIG. 32 and FIG. 33, a single LED chip 52 may becoated with a single phosphor layer 55 or single transparent resin layer56. Besides, as one of applied examples, such a multilayer structure maybe adopted that the periphery of a single or plural LED chips arecovered with a transparent resin layer, a phosphor layer is formed onthe outside of the transparent resin layer, and an additionaltransparent resin layer is formed on the outside of the phosphor layer.

In the above-described various film structures, the purpose of formingthe transparent resin layer is to average light emission intensities.When a plural of LED chips are arranged in a certain pattern, both alocation where LED chips exist and a location where no LED chip existsare present on the substrate. If the peripheries of the LED chips ofsuch a pattern are covered with a phosphor layer, the light emissionintensity is high in the part where the LED chips exist, and the lightemission intensity is low in the part where no LED chip exists. Thus, auniform light emission over the entire surface of the phosphor layercannot be obtained. At this time, if a transparent resin layer is formedon the inner surface or outer surface of the phosphor layer, it becomeseasier to obtain uniform light over the entire layer. The reason forthis is that if the transparent resin layer is formed on the innersurface of the phosphor layer, primary light from the LEDs is scatteredin the transparent resin layer. On the other hand, if the transparentresin layer is formed on the outer surface of the phosphor layer,secondary light from the phosphor is scattered in the transparent resinlayer. Aside from the case in which the number of LED chips is plural,even in the case in which the number of LED chips is one, the sameadvantageous effects can be obtained. Although a general shape of theLED chip is rectangular parallelepipedic, the light emission intensitiesof light emitted from the respective planes of the rectangularparallelepiped are not equal, and a light intensity distribution occursdepending on directions of emission. Accordingly, if the transparentresin layer is formed on the inner surface or outer surface of thephosphor layer which covers the periphery of the LED chip, the lightemission intensity can be averaged, like the case in which the number ofLED chips is plural.

As described above, the averaging of light emission intensity isobtained by the light scattering effect in the transparent resin layer.A greater scattering effect is exhibited by using, instead of a simpletransparent resin layer, a resin layer in which particulate inorganiccompound powder is contained. Examples of the inorganic material powder,which is contained in the resin layer, include silica powder such asfumed silica (dry silica) or precipitated silica (wet silica), aluminapowder such as fumed alumina or pulverized alumina, and metal oxidepowder such as cerium oxide powder, zirconium oxide powder, titaniumoxide powder or barium titanate powder. One kind or two or more kinds ofinorganic materials can be used. Of these inorganic materials, thesilica powder and alumina powder are preferable as an inorganic compoundpowder to be contained in the transparent resin layer, since the silicapowder and alumina powder are inexpensive and can easily be made intofine particles. In particular, fumed silica and fumed alumina aresuitable since spherical ultra-fine particles can easily be obtained.

In addition, it is preferable that the maximum particle size of theinorganic material powder is ¼ or less of the wavelength of lightpassing through the transparent resin layer. If the inorganic compoundpowder having the maximum particle size of ¼ or less of the wavelengthof light is used, the passing light is properly scattered, the intensityof light emitted from the light source is averaged, and the lightdistribution can be improved. When the maximum particle size exceeds ¼of the wavelength of light, it is highly probable that the light emittedfrom the LED or phosphor is reflected by fine particles of the inorganicmaterial, and is returned to the inside of the light source (the LEDchip side). The lower limit value of the maximum particle size of theinorganic material powder is not particularly limited from the aspect ofthe scattering effect. However, it is difficult to obtain extremely fineparticles from the industrial aspect. Besides, from the aspect ofhandling of powder, the lower limit value of the maximum particle sizeshould preferably be greater than several nm, and more preferably beseveral-ten nm or more.

A concrete maximum particle size of the inorganic material powder is 140nm or less for yellow light of 560 nm, and is 105 nm or less for violetlight of 420 nm. The minimum wavelength of passing light is ultravioletin a case of using an LED having a light emission peak at 360 nm. Ifinorganic material powder having the maximum particle size of 90 nm isused, this inorganic material powder is adaptive to transparent resinlayers in all cases.

It is preferable that the above-described inorganic compound powder iscontained in the transparent resin layer in a range of 0.1 to 5 mass %.If the content of inorganic compound powder in the transparent resinlayer is less than 0.1 mass %, there is concern that the lightscattering effect by the inorganic compound powder cannot fully beobtained. On the other hand, if the content of inorganic compound powderin the transparent resin layer exceeds 5 mass %, multiple scattering oflight, or the like tends to easily occur, and there is concern that theamount of light extracted to the outside of the light source decreases.It is more preferable that the content of inorganic compound powder inthe transparent resin layer is 1 mass % or more.

The phosphor layer may contain a transparent resin material. On theother hand, the transparent resin layer may mainly consist of atransparent resin material, but may contain some other component such asa phosphor or inorganic material powder. Any kind of such transparentresin material may be used if the material has sufficient strength, heatresistance and transparency. Concretely, it is preferable to usesilicone resin, epoxy resin, etc. In particular, like the presentinvention, when the transparent resin layer is used in combination withthe LED of ultraviolet emission, it is more preferable to use siliconeresin which is excellent in characteristic of resistance to degradationdue to ultraviolet.

When the silicone resin is used as the transparent resin material, it ispreferable to use, for the substrate material, an alumina substratehaving a water absorption coefficient in a range of 5 to 60%. By usingthe alumina substrate having a proper water absorption coefficient, thestrength of adhesion to the silicone resin-containing layer (e.g.,silicone resin-containing transparent resin layer and siliconeresin-containing phosphor layer) is improved. Specifically, the adhesionstrength between the alumina substrate and silicone resin-containinglayer can be set at 1 N (100 gf) or more. It is assumed that the waterabsorption coefficient of the alumina substrate indicates a valuemeasured by a water absorption coefficient evaluation method disclosedin EMAS-9101. It is assumed that the adhesion strength between thealumina substrate and the silicone resin-containing layer indicates apushing force at a time when the silicone resin-containing layer(phosphor layer) was pushed from the side surface thereof by a tensiongauge, and the silicone resin-containing layer (phosphor layer) waspeeled.

According to the alumina substrate having the water absorptioncoefficient of 5% or more, since silicone resin is properly permeatedtherein, the strength of adhesion to the silicone resin-containing layercan be enhanced. When the water absorption coefficient of the aluminasubstrate is less than 5%, the permeation of silicone resin is weak, anda sufficient adhesion strength cannot be obtained. However, if the waterabsorption coefficient of the alumina substrate exceeds 60%, thesilicone resin is excessively permeated, and it becomes difficult toform the silicone resin-containing layer (phosphor layer) in apredetermined shape. It is more preferable that the water absorptioncoefficient of the alumina substrate is in a range of 20 to 50%.

The water absorption coefficient of the alumina substrate can beadjusted, for example, by varying the firing temperature at a time ofbaking the substrate. Concretely, in accordance with the material forforming the alumina substrate, etc., the temperature at a time of bakingthe substrate is properly adjusted in a range of 1100 to 1500° C.Thereby, the alumina substrate having a proper water absorptioncoefficient (in a range of 5 to 60%) can be obtained.

By using the above-described alumina substrate, the adhesion strengthbetween the alumina substrate and the silicone resin-containing layercan be set at 1 N or more. The same applies to the case in which atransparent silicone resin-containing layer is interposed between theLED chip and phosphor layer, and the adhesion strength between thealumina substrate and the transparent silicone resin-containing layercan be set at 1 N or more. In this manner, by setting the adhesionstrength between the alumina substrate and the silicone resin-containinglayer or transparent silicone resin-containing layer at 1 N or more, thehandling efficiency of the LED module is enhanced. Specifically, thepeeling of the silicone resin-containing layer at a time of handling issuppressed. Therefore, a failure in lighting or damage due to thepeeling of the silicone resin-containing layer can be suppressed, whilegood reproducibility is obtained.

EXAMPLES

Hereinafter, methods of successively reproducing the variations ofsunlight and methods of reducing ultraviolet and blue light components,which are included in white light to be reproduced, will be concretelydescribed.

Example 1

To begin with, six kinds of white light sources were formed by combiningfour kinds of phosphors, namely a blue phosphor, a green phosphor, ayellow phosphor and a red phosphor, and an LED. Specifically, phosphorswith compositions described in Table 1-2 were mixed at predeterminedratios described in the Table, and white lights of six kinds of colortemperatures were obtained. Powder with an average particle size of 25to 35 μm was used for each phosphor, and a slurry in which the powderwas dispersed in a silicone resin was applied to the periphery of an LEDchip. Thereby, an LED module was formed. The thickness of the phosphorlayer was adjusted in a range of 500 to 700 μm, and the density of thephosphor powder in the phosphor layer was adjusted in a range of 70 to80 mass %. In addition, a GaN-based LED having a light emission peak at410 nm was used as the LED. A reflector, a lens and a cover wereattached to this LED module, and electronic circuit was connected to theLED module. Thus, white light sources of this Example were prepared.

TABLE 1-2 Light source Blue phosphor Green phosphor Yellow phosphor Redphosphor No. Color temperatures Wt % Wt % Wt % Wt % 1 2000K + 0.0075 duveuropium activated europium activated europium activated europiumactivated alkaline earth strontium sialon orthosilicate calciumphosphate phosphor phosphor phosphor nitridoaluminosilicate phosphor 824 4 10 2 3200K + 0.0075 duv europium activated europium activated ceriumactivated rare europium activated barium magnesium β-sialon phosphorearth aluminum garnet strontium sialon aluminate phosphor phosphorphosphor 84 3 4 9 3 6500K + 0.0125 duv europium activated europiumactivated europium activated europium activated alkaline earthorthosilicate orthosilicate calcium phosphate phosphor phosphor phosphornitridoaluminosilicate phosphor 92 3 4 1 4 6500K − 0.0040 duv europiumactivated europium activated cerium activated rare europium activatedalkaline earth orthosilicate earth aluminum garnet strontium sialonphosphate phosphor phosphor phosphor phosphor 95 2 1 2 5 3100K − 0.0050duv europium activated europium activated europium activated europiumactivated barium magnesium strontium sialon orthosilicate calciumaluminate phosphor phosphor phosphor nitridoaluminosilicate phosphor 853 2 10 6 2000K − 0.0050 duv europium activated europium activated ceriumactivated rare manganese activated alkaline earth β-sialon phosphorearth aluminum garnet magnesium phosphate phosphor phosphorfluorogermanate phosphor 86 2 2 10

Next, using the above six kinds of white light sources, a one-dayvariation of sunlight at a specific place was reproduced. The reproducedvariation is a one-day variation in Yokohama in spring (May 14, 2015).The data used for reproduction are data obtained by measuring sunlightemission spectra for about every three minutes from sunrise to sunset inthe same day. Of these data, FIG. 5 extracts and shows light emissionspectra of sunlight at 7:00 a.m., 12:00 p.m. and 6:45 p.m. in the sameday. With respect to the sunlight at the three kinds of time instants,the respective correlated color temperatures were calculated based onthe light emission spectrum data. The results of calculation were 4236K+0.004 duv at 7:00 a.m., 5704 K+0.001 duv at 12:00 p.m., and 2990K−0.004 duv at 6:45 p.m.

To begin with, the sunlight emission spectra at the three time instantswere reproduced by using the above six kinds of white light sources(white light sources 1 to 6) of the present invention. The mixtureratios of the respective light source colors are as shown in Table 2.The numerals in the Table indicate intensity ratios (relative values).In addition, light emission spectral distributions of three kinds ofwhite light sources are as shown by curves 6 to 8 in FIG. 6. If theselight emission spectrum shapes are compared with light emission spectraof blackbody radiation of the same color temperature, it is understoodthat the overall shapes of both show good agreement, aside frommicroscopic irregularities appearing in the light emission spectrumcurves. In particular, in the wavelength range of 400 nm to 650 nm towhich human eyes have high sensitivity, both showed very similar curves.

TABLE 2 Time Light Light Light Light Light Light instant source 1 source2 source 3 source 4 source 5 source 6 A 07:00 40 — — — 25 35 B 12:00 —40 10 20 30 — C 18:45 40 — — —  5 55

With respect to the light emission spectra of light sources A to C andthe light emission spectra of blackbody radiation of the same colortemperatures as the correlated color temperatures of the respectivelight sources, difference spectra between both were calculated. Thedifference spectrum is obtained as follows. When P(λ) is the lightemission spectrum of each white light source; B(λ) is the light emissionspectrum of blackbody radiation having the same color temperature as thewhite light source; V(λ) is the spectrum of a spectral luminousefficiency; λmax1is the wavelength at which P(λ)×V(λ) becomes largest;and λmax2 is the wavelength at which B(λ)×V(λ) becomes largest,

[(P(λ)×V(λ))/(P(λmax1)×V(λmax1))−(B(λ)×V(λ))/(B(λmax2)×V(λmax2))]

is calculated. The difference spectrum is obtained by plotting thecalculated value over the visible light wavelength range of 380 nm to780 nm. As is understood from FIG. 7 to FIG. 9, with respect to each ofthe light sources A, B and C, the difference spectrum is in the range of±0.1 or less, and satisfies the above expression (3). Thus, each of thelight sources has characteristics suitable for the white light source ofthe present invention.

Next, the color rendering indexes of these light sources werecalculated. With respect to the three kinds of light sources, the dataof each spectrum intensity was calculated at intervals of 5 nm over thewavelength range of 380 nm to 780 nm. Then, calculations were madeaccording to the method described in JIS-8726, and the average colorrendering index and special color rendering indexes were calculated. Theresults are shown in Table 3 below. The white light sources of Example 1indicate high values in all evaluation indices, and exhibit excellentcolor rendering properties which are substantially equal to those ofsunlight.

TABLE 3 Ra R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 Lightsource A 97.3 97.6 97.7 98.0 97.3 97.6 96.0 97.0 97.1 90.5 95.1 96.094.7 97.2 98.9 98.8 Light source B 98.4 98.1 98.6 99.7 98.6 98.2 97.698.1 98.4 98.5 97.7 97.9 91.4 98.0 99.4 98.0 Light source C 97.5 97.798.5 99.0 96.6 97.3 96.0 98.0 96.9 87.0 97.7 93.6 94.9 97.4 98.6 99.4

Each of the white light sources of Example 1 employs the LED module inwhich the violet emission LED having the light emission peak at 410 nmand the four kinds of phosphors are combined. In general, the LED has alight emission spectrum having a sharp shape at a light emission peakwavelength, and the phosphor has a broad light emission spectrum. Thus,the whole spectrum shape tends to become unnatural, with a spike oflight emission of the LED. However, the light emission peak of the LEDused in Example 1 exists not in the blue region but in the violetregion. Blue light is not conspicuous, and most of violet light emittedfrom the LED is absorbed by the phosphor. Thus, the amount of LED lightleaking to the outside of the module is small. Therefore, the whitelight source of the present invention can be configured as a white lightsource which is kind to human bodies, with no fear of blue lighthazards, etc.

As regards the white light sources of the present invention, in order toquantitatively evaluate the above advantageous effects, the value ofP(λ)/B(λ) of each white light source was obtained by calculation. If thelight source C is taken as an example, the calculation method of theP(λ)/B(λ) value is as follows. To begin with, the light emissionspectral distribution of the light source C is measured by using aspectral distribution measuring device. Various kinds of devices haverecently been commercially available as the spectral distributionmeasuring device. If there is no problem with precision, the type ofdevice does not need to be particularly restricted. A concrete shape ofthe light emission spectrum is as shown by the curve 8 in FIG. 6, asalready described, and this emission spectrum is set as P(λ). If a lightemission color temperature point on the xy chromaticity diagram iscalculated by using the light emission spectral distribution data ofthis P(λ), it is understood that the light source C is a white lightsource of a correlated color temperature of 2990 K−0.004 duv.Accordingly, the light emission spectrum B(λ) of the correspondingblackbody has the color temperature of 2990 K. Hence, by substituting2990 K for the color temperature (T) in the above equation (6), theconcrete spectrum shape can be obtained.

By comparing the light emission intensities of the obtained P(λ) andB(λ), the P(λ)/B(λ) value can be calculated. However, if the obtainedlight emission spectral distributions are compared as such, the resultwill vary in any way, depending on the method of calculation. Thus, bysetting a condition under which the total energy of both becomes anidentical value, the P(λ) and B(λ) which satisfy this condition werecalculated, and then both were compared. The concrete condition is thatthe following equation (1) is satisfied:

$\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1)\end{matrix}$

In the equation, V(λ) is the spectral distribution of the spectralluminous efficiency, and each spectral distribution of the P(λ) and B(λ)which satisfy the above equation (1) was obtained by calculation. If theP(λ) and B(λ) after correction are shown together in one graph, spectraldistributions shown in FIG. 10 are obtained. A curve 9 is B(λ) aftercorrection, and a curve 10 is P(λ) after correction.

In FIG. 10, if intensities of both spectral distributions are comparedin the range of 400 nm to 495 nm, there are approximately three pointswhere the emission intensity of P(λ) exceeds the emission intensity ofB(λ). In such wavelength regions, if the maximum value of the P(λ)/B(λ)ratio is calculated, the value of 1.37 was obtained. This means that, inall wavelengths of 400 nm to 495 nm, the emission intensity of P(λ) is1.37 times or less the emission intensity of B(λ).

In the present invention, as regards the P(λ)/B(λ) of each white lightsource, the maximum value of the P(λ)/B(λ) ratio as calculated in theabove is adopted as a representative value, and is set as an evaluationreference of each white light source. Specifically, if the P(λ)/B(λ)value exceeds 1 and indicates a greater value, this means that anexcessive and large amount of visible light of 400 nm to 495 nm includedin each white light source, in particular, blue light, is includedrelative to the visible light of the same wavelength range included inthe light emission spectrum of the blackbody. From the above, it isunderstood that the light source C satisfies the relationship of thefollowing expression (9) in the wavelength range of 400 nm to 495 nm:

P(λ)/B(λ)≤1.37   (9)

If the same relationship is confirmed with respect to the light sourcesB and A in Table 3, spectral curves of FIG. 11 and FIG. 12 can beobtained. It was found that the light source B satisfies the followingexpression (10):

P(λ)/B(λ)≤1.26   (10)

and that the light source A satisfies the following expression (11):

P(λ)/B(λ)≤1.07   (11)

Accordingly, the white light sources C, B and A are regarded as lightsources which exhibit smooth light emission spectra with lessirregularities in the blue wavelength region, and scarcely exert aharmful effect on the circadian rhythms of human bodies.

In addition, in the LED modules of Example 1, the amount of ultravioletleaking from the module is reduced. When the LED primary lights leakingfrom the light sources of the Example were calculated by using the aboveequations (7) and (8), the LED primary lights were all 0.1 mW/lm, andwere very weak. Accordingly, when the white light sources of Example 1were used as illumination for works of art or the like, the pigments orthe like used in the works of art were not deteriorated. When the whitelight sources of Example 1 were used as illumination for human bodies,the skin or eyes of human bodies were not damaged, and suitableillumination for these purposes was successfully obtained.

In the above, the various characteristics of the white light sources ofExample 1 were described. However, only typical white lights of themorning, daytime and evening were described. Actually, the white lighthaving the above characteristics can be reproduced as light with one-daycontinuous variations. FIG. 13 is a graph showing one-day variations inYokohama in spring (May 14, 2015). Using the light emission spectrumdata of sunlight measured every three minutes, the values of respectivecorrelated color temperatures were calculated, and sunlight wasreproduced by determining the mixture ratio of the light source 1 tolight source 6 such that predetermined correlated color temperatures canbe obtained. In addition, based on the actual measurement data, thevariation of illuminance was plotted as an illuminance ratio (%), bycalculating relative values with reference to a certain value.

In FIG. 13, a curve 15 indicates the variation of the correlated colortemperature, and a curve 16 indicates an illuminance variation. Theone-day variation in Yokohama in spring was such that the illuminancebecame brighter with the sunrise, the illuminance took a maximum valueat around 11:00 a.m. and then remained high until after 1:00 p.m., andthe illuminance gradually decreased toward sunset. On the other hand, asregards the color temperature, the sun in crimson of about 2200 Kappeared at sunrise, the color temperature increased in accordance withthe increase of illuminance, warm white changed to white and to daylightwhite, and the color temperature reached about 6000 K at maximum ataround 12:00 p.m. Thereafter, with the progress reverse to the morning,the color temperature decreases back to 2300 K at around 7:00 p.m., andthen the sun set.

In the white light source system of the present invention, thevariations with time of the color temperature and illuminance shown inFIG. 13 were reproduced by controlling the values of electric currentsapplied to the white light sources. To begin with, in order to obtainwhite light of a correlated color temperature, the intensity ratio ofelectric currents applied to the light source 1 to light source 6 wasdetermined. Next, in order to adapt to the variation of illuminance, theintensity of the total electric current was adjusted such that apredetermined illumination can be obtained while the above-describedcurrent ratio is maintained. In the white light source of the presentinvention, the program control of current values is executed such thatthe data of the variation with time shown in FIG. 13 can be adjustedbased on the actual measurement values every three minutes, and thevariation with time of the sunlight was reproduced.

This white light source system was applied as illumination for an artmuseum, a hospital, and a home. In this illumination, instantaneouscharacteristics of sunlight are not reproduced, but light emissioncharacteristics, which vary from time to time, are reproduced. Goodinfluence on the circadian rhythms which human bodies have can beexpected. Moreover, in the characteristic variation of whiteillumination, gentle variations, which are not perceptible to humaneyes, are reproduced. Thus, such variations are perceived by humans asvery natural variations like sunlight. Accordingly, even inpatients orthe like, who are physically weak, can accept the reproduced light asnatural illumination.

Comparative Example 1

A white light source of a specific color temperature, which is locatedon the locus of blackbody radiation, was created, regardless of thespectrum shape of sunlight. A LED module, which was used, is acombination of a blue LED and a yellow phosphor. An InGaN-based LEDhaving a light emission peak wavelength at 448 nm was used for the LED.A europium activated orthosilicate phosphor having a peak wavelength at560 nm was used for the phosphor. The average particle size of thephosphor was 7 μm. A phosphor slurry was created by dispersing thephosphor particles in a silicone resin. The slurry was uniformly appliedin a manner to cover the LED chip disposed on the substrate. Thereby,the LED module was formed. The film thickness of the phosphor layer wasabout 65 μm, as a result of adjustment to such a thickness that desiredwhite light is obtained by mixing blue light of the LED and yellow lightof the phosphor.

A reflector, a lens and a cover were attached to this LED module, andelectronic circuit was connected to the LED module. Thus, a white lightsource of this Comparative Example was fabricated. The color temperatureof the obtained white light source was 6338 K, and the light emissionspectrum characteristic, (P(λ)×V(λ)/(P(λmax1)×V(λmax1)), was as shown inFIG. 14. In addition, as regards the blackbody radiation spectrum of thecorresponding color temperature of 6338 K, ifB(λ)×V(λ)/(B(λmax2)×V(λmax2)) is calculated, a curve shown in FIG. 15was obtained. Furthermore, a difference spectrum between FIG. 14 andFIG. 15, (P(λ)×V(λ)/(P(λmax1)×V(λmax1))−B(λ)×V(λ)/(B(λmax2)×V(λmax2)),is as shown in FIG. 16. As is understood from FIG. 16, the differencespectrum is distributed in the range of −0.32 to +0.02. The absolutevalue of the difference spectrum fails to satisfy the condition of 0.2or less in the entire wavelength range, and the spectrum of sunlight wasnot reproduced.

The white light source of Comparative Example 1 agreed with the colortemperature on the locus of blackbody radiation. However, since thelight emission spectrum shape was different, such high color renderingproperties as sunlight could not be exhibited. The average colorrendering index Ra was as low as about 70, and R₁ to R₁₅ were as shownin the Table below, which were very different from the characteristicsof sunlight.

TABLE 4 Ra R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15Comparative 69.6 68.3 73.4 72.6 70.7 61.9 91.8 79.3 61.6 24.9 32.7 65.138.1 68.2 84.1 65.8 Example 1

Subsequently, with respect to the white light source of ComparativeExample 1, the characteristics of the blue wavelength region wereconfirmed. Assuming that the light emission spectrum of the white lightsource of Comparative Example 1 is P(λ), the light emission spectrumdistribution of blackbody radiation having the corresponding correlatedcolor temperature is B(λ), and the spectrum of the spectral luminousefficiency is V(λ), when these satisfy the following equation (1):

$\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1)\end{matrix}$

the light emission spectrum of the white light source of ComparativeExample 1 exhibited a relationship of the following expression (12) in awavelength range of 400 nm to 495 nm:

P(λ)/B(λ)≤1.87   (12)

and the P(λ)/B(λ) value exceeded the upper limit value of 1.8 of thewhite light source of the present invention. Concretely, this is asshown in FIG. 17. As is understood from FIG. 17, the white light sourceof Comparative Example 1 has a sharp light emission spectrum shapehaving a peak in the neighborhood of 450 nm. Compared to the lightemission spectrum shape of blackbody radiation, this spectrum shape hasan excessive projection portion near 450 nm and has an excessive recessportion before 500 nm, and this light emission spectrum had clearlydifferent characteristics from the blackbody radiation (sunlight). Inthe meantime, the white light source using the blue LED is characterizedby such a conspicuous projection portion. As the color temperature ofthe white light source becomes lower, this projection portion becomesmore conspicuous. Accordingly, although the white light source ofComparative Example 1 was the white light source of the colortemperature which is as high as 6338 K, there is a tendency that if thecolor temperature becomes lower, the P(λ)/B(λ) value becomes greaterthan 1.87.

In this manner, the white color source of Comparative Example 1apparently exhibited the same white light emission as the presentinvention, but exhibited characteristics which are poor in redness andhave a low color rendering property. When such a white light source isused as illumination for a hospital, since a strong light emissionwavelength component is included in the blue region, there is concernabout the problem of blue light hazards, etc., and the harmful effect oncircadian rhythms of human bodies. Besides, in the white light source ofComparative Example 1, since the blue light emission LED was used as theLED module, little ultraviolet is included in the white light source ofComparative Example 1. However, if an ultraviolet light emission LED isused, it is clear that a great amount of ultraviolet leaks. If theultraviolet light emission LED is used as illumination for an artmuseum, there is concern about harmful effects as a matter of course,such as increased fading of paintings. Incidentally, since the lightemission characteristics of the white light source of ComparativeExample 1 are too greatly different from those of sunlight in everyaspect, it is meaningless to reproduce one-day sunlight variations byusing the white light source of Comparative Example 1. Thus, a whitelight source system, which uses such a white light source, was notcreated.

Example 2

Evaluation experiments were conducted as to how the blue light emissioncomponent included in the white light source of the present invention isperceived by human bodies. In the present invention, as regards theintensity of blue light included in the white light source, theP(λ)/B(λ) value shown in the above equation (1) is used as a criterionof evaluation. If this numerical value is as close as possible to 1,this value is a most desirable value, judging comprehensively from theaspects of the color rendering property of the illumination light sourceand the safety to human bodies. On the other hand, from the aspect ofsafety, it is preferable that this numerical value is as small aspossible. Confirmation experiments were conducted as to what values aretolerable as the upper limit value.

In the experiments, white light sources of various P(λ)/B(λ) values wereprepared. The degree of influence on human bodies was examined bydetermining how much dazzle a person, who views light emitted from thewhite light source, perceives. Specifically, if the fact that adifference occurs in the degree of perception of dazzle in a human bodydue to a difference in intensity of blue light can be confirmed, thisbecomes evidence that the blue light has such influence on human bodies.The problem here is the method used in the experiment. The perception ofdazzle by a human, who views the light source, is influenced by theintensity of light from the light source. The light source, which is theobject of experiments, is the white light source. Even if dazzle of acertain white light source was specified, it is necessary to make itpossible to first confirm that the cause of dazzle is not the overallintensity of the white light or the intensity of a red light emissioncomponent or the like, but the cause of dazzle is the intensity of ablue light emission component. Then, it is necessary that a correlationbe recognized between the degree of perceived dazzle and the variationin intensity of the blue light component.

In the present invention, the physical characteristics of blue light areutilized as a method for evaluating the degree of influence of bluelight upon eyes, by distinguishing this degree of influence from thedegree of influence of other visible light. The light emission componentof the wavelength range of 400 to 495 nm including blue light has higherenergy than the visible light components of other wavelengths. Ingeneral, electromagnetic waves having high energy tend to collide withvarious obstacles while traveling through space and tend to be easilyscattered. In short, it is known that blue light is scattered moreeasily than other visible light components. Thus, of the emission lightemitted from the white light source, a blue light emission component isscattered by the influence of floating matter such as gas molecules anddust in the air, and, at the same time, the blue light reaching theinside of the eye strongly undergoes the influence of scattering whiletraveling through the crystal lens. On the other hand, vision cells ofthe retina, which the blue light reaches after passing through thecrystal lens, are composed of cones, which are mainly located in acentral part of the retina and which normally perceive a bright image,and rods, which are mainly located in a peripheral part of the retinaand which perceive a dark image. Thus, scattered blue light reaches rodswhich normally sense a dark image. If bright scattered light that is notnormally sensed by the rods reach the rods, the sphincter muscle of thepupil excessively contracts, and a human strongly senses dazzle.

Due to the above phenomenon, when a human senses dazzle, the sense ofdazzle occurs mainly because excessive light reaches the rods in thecase of blue light, while the sense of dazzle occurs mainly becauseexcessive light reaches the cones in the case of visible light otherthan blue light. Thus, the mechanism of sensing dazzle differs betweenboth cases. Accordingly, by utilizing this phenomenon, for example, theoverall intensity of the white light source is kept constant, and thenthe content ratio of the blue light component that is a constituent ofthe white light is varied. Thereby, the degree of dazzle perceived byhumans can correctly be evaluated. Specifically, even when the amount oflight reaching the cones is constant or slightly decreases, if theamount of light reaching the rods increases, humans sense dazzle morestrongly. To measure this variation is the most effective means forevaluating the influence of blue light upon the human body.

Hereinafter, the contents of concrete experiments and the resultsthereof are summarized.

For the purpose of examination, in order to obtain light sources ofvarious P(λ)/B(λ) values, the following five kinds of light sources wereadditionally experimentally fabricated, and were used as light sourcesof the Example and Comparative Example.

To begin with, a white light source was fabricated in which the lightemission intensity of the blue wavelength region in the light emissionspectrum of white light was reduced as much as possible. Concretely, tocope with this, an ultraviolet to blue light absorption film was formedon the LED module of the light source B of Example 1. A three-layer filmwas formed on the periphery of the phosphor layer which covers theperiphery of the LED chip of the light source B of Example 1. A thinfilm (first layer) of about 3 μm, which is formed by using a zinc oxidepigment with an average particle size of 0.3 μm, was formed on theinnermost side. A film (second layer) of about 0.9 μm, which is formedby using zirconium oxide with an average particle size of 0.08 μm, wasformed in the middle. A thin film (third layer) of about 6 μm, which isformed by using silicon oxide with an average particle size of 0.5 μm,was formed on the outermost side. Each of the thin films was formed suchthat fine particle powder was dispersed in a silicone resin, thespecific gravity and viscosity were adjusted, and then a predeterminedamount of a slurry of the result was applied.

A predetermined electric current was applied to the obtained LED module,and it was confirmed that the LED module emits white light. The lightemission spectral distribution of white light emitted from the LEDmodule was measured by using the spectral distribution measuring device.Based on the obtained light emission spectrum data, a chromaticity pointon the (x, y) chromaticity diagram was calculated. The calculatedchromaticity point was 5110 K−0.002 duv. It turned out that the colortemperature shifted to a lower color temperature side by about 600 K,relative to the correlated color temperature of 5704 K+0.001 duv of thelight source B before the violet to blue component was cut.

Assuming that the light emission spectrum of the white light sourceafter the cutting of the violet to blue component is P(λ), the lightemission spectrum distribution of blackbody radiation having thecorresponding correlated color temperature is B(λ), and the spectrum ofthe spectral luminous efficiency is V(λ), when these satisfy thefollowing equation (1):

$\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1)\end{matrix}$

the ratio of P(λ)/B(λ) is 0.98 at most in the wavelength range of 400 nmto 495 nm, and the following expression (13) was successfully satisfied:

P(λ)/B(λ)<1   (13)

Specifically, when the light emission intensity of the obtained whitelight source was compared with the light emission intensity of blackbodyradiation, the light emission intensity of the light source of Example 2never exceeded the light emission intensity of blackbody radiation inthe entire wavelength range of 400 nm to 495 nm.

Next, four kinds of white light sources (4) to (7) of Example 2, whichexhibit relatively large values of the above P(λ)/B(λ) value, werefabricated. All the materials and parts used in the fabrication are thesame as those in Example 1, and the parts were assembled in the samemanner as in Example 1. Specifically, the light source colors of thewhite light sources 1 to 6 of Example 1 were mixed at mixture ratiosshown in Table 5-2. Thereby, the four kinds of white light sources (4)to (7) of Example 2 were obtained. The numerals in Table 5-2 indicateintensity ratios (relative values). The intensity ratios were controlledby controlling the values of electric currents which are applied to thewhite color sources 1 to 6. In addition, in order to evaluate theP(λ)/B(λ) values of the obtained white light sources, the light emissionspectra of the additionally experimentally fabricated white lightsources (5) to (7) were compared with the light emission spectra ofblackbody radiation corresponding to the white light sources. Then,graphs of FIG. 18, FIG. 19 and FIG. 20 were obtained. As is understoodfrom these Figures, in the respective light sources, the maximum valuesof the P(λ)/B(λ) value in the wavelength range of 400 nm to 495 nm were1.47 in the light source of FIG. 18, 1.69 in the light source of FIG.19, and 1.76 in the light source of FIG. 20.

In addition, the difference spectra of the white light sources (4) to(7) were in the range of ±0.1 or less, and satisfied the aboveexpression (3).

TABLE 5-1 Light source ★ Color temperatures P(λ)/B(λ) ★★  (1) 4236K +0.004 duv 1.07  (2) 5704K + 0.001 duv 1.26  (3) 2990K − 0.004 duv 1.37 (4) 5110K − 0.002 duv 0.98  (5) 5198K + 0.002 duv 1.47  (6) 4322K −0.002 duv 1.69  (7) 5262K + 0.001 duv 1.76  (8) 6338K + 0.005 duv 1.87 (9) 3886K − 0.001 duv 2.11 (10) 2960 − 0.0004 duv 3.28 ★ (1), (2) and(3) correspond to the light sources A, B and C of Example 1,respectively. (4) to (7) correspond to the additionally experimentallyfabricated light sources of Example 2. (8) corresponds to the lightsource of Comparative Example 1. (9) and (10) correspond to the lightsources of Comparative Example, which were additionally experimentallyfabricated in Example 2. ★★ The maximum values of the P(λ)/B(λ) ratio inthe wavelength region in which wavelength λ is 400 to 495 nm.

TABLE 5-2 Light Light Light Light Light Light source 1 source 2 source 3source 4 source 5 source 6 Light source (4) 0.09 — 0.51 0.34 — 0.06Light source (5) 0.09 — 0.70 0.18 — 0.03 Light source (6) — 0.23 0.190.23 0.35 — Light source (7) — 0.14 0.43 0.33 0.10 —

In addition, two kinds of white light sources of a Comparative Examplewere additionally experimentally fabricated. One white light source (9)of the Comparative Example is identical to Comparative Example 1 withrespect to the materials and parts which were used. However, the amountof the phosphor combined with the LED was changed by decreasing thethickness of the phosphor layer to 62 μm, and the white light sourceexhibiting a different P(λ)/B(λ) value was fabricated. A concrete lightemission spectrum shape is as shown in FIG. 21, and the maximum value ofthe P(λ)/B(λ) value in the wavelength range of 400 nm to 495 nm was2.11. In addition, the other white light source (10) of the ComparativeExample is also identical to Comparative Example 1 with respect to thematerials and parts which were used. However, the amount of the phosphorcombined with the LED was changed by decreasing the thickness of thephosphor layer to 55 μm, and the white light source exhibiting adifferent P(λ)/B(λ) value was fabricated. A concrete light emissionspectrum shape is as shown in FIG. 36, and the maximum value of theP(λ)/B(λ) value in the wavelength range of 400 nm to 495 nm was 3.28.

The various characteristics of the light sources used in thisevaluation, in addition to the above experimental products, aresummarized as shown in Tables 5-1 and 5-2. As the light sources for theevaluation, the light sources of Example 1 and Comparative Example 1, aswell as the light sources which were experimentally fabricated inExample 2, were added for the purpose of comparison. In Table 6, thecharacteristics of the color rendering indexes of the major lightsources, which were experimentally fabricated in Example 2, aresummarized in a table form.

TABLE 6 Light source Ra R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14R15 Example (5)  97.4 99.4 98.1 93.2 97.5 99.3 96.7 97.5 97.1 95.5 93.197.4 89.9 99.6 65.5 98.0 Example (6)  97.2 97.7 97.4 97.6 98.1 97.4 95.297.3 96.9 04.6 94.3 95.9 92.8 97.1 99.0 99.4 Example (7)  97.0 98.8 98.092.5 96.3 99.6 96.9 96.6 96.0 93.4 92.8 96.8 91.9 99.2 95.0 97.1Comparative 97.6 99.0 98.1 94.8 97.8 97.9 95.4 98.6 99.1 96.8 94.0 96.479.5 98.9 96.6 98.5 Example (9)  Comparative 91.2 96.3 92.9 87.3 88.793.4 90.4 89.4 91.0 85.1 82.4 90.3 78.4 94.9 91.8 94.1 Example (10)

In order to evaluate the white light sources, subjective tests by humansensation were conducted. In experiments, the ten kinds of light sourcesof the above Table 5-1 were prepared. The ten kinds of light sourceswere successively lighted under the operational condition under whichthe luminances of the light sources become equal. During the lightingtests of the light sources, the curtains of windows were closed, and thebrightness of ceiling illumination was constantly kept at a fixed valueso that the indoor illuminance may not change. In addition, a humanstands at a position at a distance of 3 m from the light sources. Thehuman directly viewed each light source, and the strength of a stimulusreceived from the light source was comparatively evaluated. In order tosimplify the criterion of evaluation, a method was adopted in which oneof two kinds of answers, “Yes” and “No”, is obtained as to whetherdazzle of each light source is sensed or not. The test subjects were 50male and female adults in total, who have normal color sensation. Asregards persons wearing eyeglasses, tests were conducted afterconfirming that they did not wear blue-cut type glasses.

With respect to the ten kinds of white light source samples, the resultsof subjective evaluation, as well as major characteristics of the lightsources, are summarized in Table 7.

TABLE 7 Ratio (%) of While persons who light Color sensed dazzle ofsources temperatures (K) P(λ)/B(λ) light sources (10)  2960 − 0.0004 duv3.28 85% (9) 3886K − 0.001 duv 2.11 68% (8) 6338K + 0.005 duv 1.87 54%(7) 5262K + 0.001 duv 1.76 44% (6) 4322K − 0.002 duv 1.69 40% (5)5198K + 0.002 duv 1.47 28% (3) 2990K − 0.004 duv 1.37 18% (2) 5704K +0.001 duv 1.26 22% (1) 4236K + 0.004 duv 1.07 14% (4) 5100K − 0.002 duv0.98 14%

The ten kinds of white light sources were comparatively evaluated underthe condition under which all of the white light sources have the sameluminance. Thus, it should be natural that the persons perceive the samedegree of dazzle with respect to all light sources. However, as shown inTable 7, the result indicates that the degree of dazzle sensed bypersons greatly differs depending on the kinds of white light sources.This result was obtained due to the peculiarity of blue light, and thisdata supports the correctness of the method of experiments. For example,as is understood from Table 7, there is a tendency that as the P(λ)/B(λ)value becomes greater, the ratio of persons who sense dazzle generallybecomes larger. This means that even if the intensity of light, which isincident on the eyes and is sensed by the eyes, is unchanged, thepersons sensed dazzle more strongly as the amount of the blue lightcomponent becomes larger, because the amount of scattering lightincreases in proportion to the amount of the blue light component.

The above phenomenon is more clearly indicated by the result ofcomparison of the combination of the two kinds of light source (1) andlight source (6) in Table 7, or the combination of the two kinds oflight source (4) and light (5) in Table 7. In these white light sources,the color temperatures of the paired light sources are substantiallyidentical. Moreover, the luminance is identical in all light sources.Thus, when humans observe these light sources, it should be natural thatboth of the paired light sources are viewed with the same brightness andcolor. Despite this, a large difference occurs in the degree ofperception of dazzle. Concretely, for example, when the light source (4)and light source (5) in Table 7 are compared, the color temperatures ofboth are about 5100 K. However, the ratio of persons who sensed dazzleof the light source (4) is 14%, while this ratio is 28% with respect tothe light source (5), and a large difference was recognized. If theP(λ)/B(λ) values of both are confirmed, this value is 0.98 in the lightsource (4), while the value is 1.47 in the light source (5). Inaccordance with the magnitude of the P(λ)/B(λ) value, the ratio ofscattering light incident on the eyes increased, thus influencing thedegree of perception of dazzle.

On the other hand, as an exception to the above, in the relationshipbetween the light source (2) and light source (3) in Table 7, aphenomenon occurs in which the relationship between the degree ofperception of dazzle by persons and the P(λ)/B(λ) value is reversed. TheP(λ)/B(λ) value of the light source (2) is 1.26 and is smaller than 1.37of the light source (3). Despite this, the ratio of persons who senseddazzle of the light source (2) is 22% which is greater than 18% of thelight source (3), and the mutual relationship was reversed. At a glance,this data is contradictory. However, such a result occurred due to thedifference between the color temperatures of white light sources. TheP(λ)/B(λ) value defines the amount of blue light which is excessivelyincluded, compared to the corresponding blackbody radiation. However,the color temperature of blackbody radiation, which is a reference forcomparison, is 2990 K in the light source (3), while this colortemperature is 5704 K in the light source (2). In general, as the valueof the color temperature of white light becomes higher, the relativeratio of the blue light component increases. Accordingly, in thespectrum of blackbody radiation which was a reference for comparisonwhen the P(λ)/B(λ) value was calculated, the blue light component of thelight source (2) was greater than the blue light component of the lightsource (3). Thus, although the excess blue light relative to theblackbody radiation was greater in the light source (3), the entireamount of blue light was greater in the light source (2). There is nodifference in the fact that the degree of perception of dazzle varies inaccordance with the content of blue light.

From the above result, it was confirmed that the content of the bluelight component in the white light source influences the degree ofperception of dazzle by humans, and that as the P(λ)/B(λ) value becomesgreater, more dazzle is perceived by humans. This result is the contentthat supports the initial assumption, and the influence by the excessblue light emission component is considered to be particularly importantas the factor by which the white light source was perceived as dazzling.In addition, in the white light sources (8) to (10) of the ComparativeExample, the P(λ)/B(λ) values are 1.87, 2.11 and 3.28, which exceed 1.8and are large values. The level of these values is such that more thanhalf the test subjects sensed dazzle of blue light. The light source,with which dazzle is so strongly sensed, is an illumination for whichthere is concern about problems of blue light hazards or the like, whichhave attracted attention in recent years. In connection with this lightsource, the investigation of the truth and the study for improvementsare to be expected in the future. On the other hand, in the white lightsources of the Example, the P(λ)/B(λ) values are in the range of 0.98 to1.76, and an improvement has been made so as to make the blue componentsmaller than in the conventional light sources of the ComparativeExample. Moreover, the ratio of persons sensing dazzle is less than 50%,and it is judged that the light of the white light sources of theExample has been improved with respect to the problems of blue lighthazards or the like.

In the meantime, in Table 5-1 and Table 5-2, in the white light sourcesof the Examples which were shown by way of example, the colortemperatures are 2990 K to 5704 K and the P(λ)/B(λ) values are in therange of 0.98 to 1.76. However, the white light sources of the presentinvention are characterized in that the color temperatures are in therange of 2000 K to 6500 K, and the P(λ)/B(λ) values are in the range of1.8 or less. Accordingly, the content of the blue light component in thewhite light source of the present invention is less than that in thewhite light source of Comparative Example 1 which is the conventionallight source. This is because the color temperature of the white lightsource of Comparative Example 1 is 6338 K and is substantially close tothe upper limit value. On the other hand, since the color temperature ofthe white light source of the present invention is substantially equalto or less than the color temperature in Comparative Example 1, thecontent of the blue light component is equal to or less than that inComparative Example 1. Besides, since the P(λ)/B(λ) value is less thanin Comparative Example 1, the content of the blue light component in thewhite light source of the present invention is surely less than that inthe white light source of Comparative Example 1. In addition, in thewhite light source (e.g., white light source V) of this invention inwhich the P(λ)/B(λ) value is 1.5 or less, the ratio of persons sensingdazzle is substantially halved, compared to the ratio with respect tothe light source of Comparative Example 1, and the influence of the bluelight component can be reduced more conspicuously. In this manner, thewhite light source of the present invention has obvious effects ofimprovement, compared to the conventional light source that is theComparative Example.

Example A

A white light source system, which is composed of four kinds of whitelight sources, was fabricated. In this system, the number of white lightsources, which constitute the system, is limited to a minimum necessarynumber. Thus, the range, in which the spectrum of blackbody radiationcan be accurately reproduced, becomes narrow. Concretely, this system isa white light source system including light sources 7 to 10 shown inFIG. 37. In a rectangular color temperature region surrounded by thelight source 7 to light source 10 in the Figure, that is, in a range ofcolor temperatures of 4500 K to 6500 K, correlated color temperatureswithin a deviation of ±0.005 duv can be reproduced. In this system, itis difficult to reproduce one-day variations of sunlight. However, sincethe system covers the range of color temperatures enough to reproducethe brightly shining sun of daytime, the system has sufficientcharacteristics for utilization as high color rendering illumination in,for example, offices.

The four kinds of white light sources were fabricated in the followingprocedure. As illustrated in FIG. 38, on an alumina substrate 71 havingan outside shape of 30×30 mm, LED chips 72 each having a chip shape of0.4×0.4 mm were disposed in a 5 (in series)×5 (in parallel) matrix. Forthe LED, GaN of violet light emission having a light emission peakwavelength at 405 nm was used. In addition, in the LED module 70 shownin FIG. 38 in which the alumina substrate having a water absorptioncoefficient of 20 to 30% was used, each of chip columns, in which theLED chips 72 are connected in series, is independently covered with atransparent resin layer (not shown), and the entire surface of each ofthe transparent resin layers of the plural columns is covered with aphosphor layer 73. In the meantime, in the transparent resin layer,fumed silica with an average primary particle size of 7 nm and a maximumparticle size of 25 nm was added as fine particle silica powder in anamount of 3 mass % relative to the transparent resin. In addition, aseach phosphor powder which is contained in the phosphor layer, phosphorpowder with an average particle size of 30 to 40 μm was used. Thetransparent resin layer was formed by applying a slurry, in which fineparticle silica powder is dispersed in silicone resin, to the peripheryof the LED chip. Then, the phosphor layer 73 was formed by applying aslurry, in which phosphor powder is dispersed in silicone resin, to theentire surface of the transparent resin layer. The thickness of thephosphor layer 73 was set at 500 to 750 μm, and the density of phosphorpowder in the phosphor layer was adjusted to fall within the range of 75to 85 mass %. In addition, a conductor 75 is formed as an electrode onthe substrate 71, and each LED chip 72 is connected to the electrode. Asthe material of the electrode, Pd metal was used. In order to protectthe electrode material, an Au film was formed on the surface of theelectrode by a printing method. A dam 74 is disposed in a manner tosurround the columns of LED chips 72 on the substrate 71. A reflector, alens and a cover were attached to this LED module 70, and electroniccircuit was connected to the LED module 70. Thus, white light sourcesincluded in the white light source system of Example A were fabricated.

Each white light source is a combination of four kinds of phosphors,namely a blue phosphor, a green phosphor, a yellow phosphor and a redphosphor, and an LED. The kinds and mixture ratios of the respectivephosphors, and the correlated color temperatures of the obtained lightsources are as shown in Table 8 below.

TABLE 8 Light source Color Blue phosphor Green phosphor Yellow phosphorRed phosphor No. temperatures Wt % Wt % Wt % Wt % 7 4500K + 0.006 duveuropium activated europium activated europium activated europiumactivated alkaline earth phosphate strontium sialon phosphororthosilicate phosphor calcium phosphor nitridoaluminosilicate phosphor80 3 11 6 8 6500K + 0.006 duv Europium activated europium activatedeuropium activated europium activated alkaline earth phosphate β-sialonphosphor orthosilicate phosphor strontium sialon phosphor phosphor 89 26 3 9 6500K − 0.005 duv Europium activated europium activated europiumactivated europium activated alkaline earth phosphate orthosilicatephosphor orthosilicate phosphor calcium phosphor nitridoaluminosilicatephosphor 92 1 4 3 10 4500K − 0.005 duv Europium activated europiumactivated europium activated europium activated alkaline earth phosphateorthosilicate phosphor orthosilicate phosphor strontium sialon phosphorphosphor 83 3 7 7

FIG. 39 to FIG. 42 show graphs in which light emission spectra of thefour kinds of white light sources are compared to the spectra ofblackbody radiation of the corresponding color temperatures. As isunderstood from FIG. 39 to FIG. 42, the spectra of the four kinds oflight sources agree with the spectra of blackbody radiation to a highextent. Difference spectra between the respective white light sourcesand the corresponding blackbody radiation spectra were calculated. Inall of the four kinds, the difference spectra are in the range of ±0.2or less, and it was confirmed that the relational expression (3) issatisfied. Accordingly, each of the light sources has characteristicssuitable for the white light source of the present invention, and whitelight obtained by mixing white lights of the four kinds is also suitablefor the white light source of the present invention, and can reproducesunlight.

In addition, as regards the mixed white light obtained by mixing thefour kinds of white light sources, the P(λ)/B(λ) values obtained by theabove relational expressions (2) and (5) were confirmed. As an example,the four kinds of light sources were mixed at an intensity ratio oflight source 7: light source 8: light source 9: light source10=0.14:0.41:0.34:0.11. Thus, a light source 11 was obtained. Thecorrelated color temperature of the mixed white light source was 6000K+0.001 duv. If the spectrum shape is compared with the spectrum ofblackbody radiation of the same color temperature, the comparison resultis as shown in FIG. 44. As is understood from FIG. 44, the P(λ)/B(λ)value is 1.17, and it was confirmed that the light source satisfies eachof the relational expression (2) and relational expression (5).

In the meantime, as shown in FIG. 39 to FIG. 42, the light emissionspectra of the white light sources of the present invention can exhibitcontinuous spectra without a break over the wavelength range of 380 nmto 780 nm. Here, the continuous spectrum means a spectrum which does notinclude, in this wavelength range, a planar wavelength region where thelight emission intensity is substantially zero.

In order to confirm the feature of the light emission spectra of thewhite light sources of the present invention, for example, the lightemission spectrum of FIG. 39 of the light source of the presentinvention is compared with the light emission spectrum shape of FIG. 17of the light source of Comparative Example 1, which was fabricated inExample 1. One to three recess portions are observed in the curves ofboth spectra. Such a recess portion occurred due to a gap betweenneighboring two kinds of light emission spectra. The reason why thelight emission intensity at the bottom of the recess portion does notbecome zero is that a long wavelength end of a short wavelength-sidelight emission spectrum and a short wavelength end of a longwavelength-side light emission spectrum overlap. The reason why thedegree of irregularity of the spectrum curve is less in the light sourceof the present invention than in the light source of the ComparativeExample is that the area of overlap between light emission spectra islarge. This effect occurs by making as close as possible the lightemission spectra with large half-value widths. By further selecting thekinds of phosphors in such a combination, re-absorption betweenphosphors becomes easier to occur, and also double excitation or thelike becomes easier to occur. The light emission color variation duringcontinuous lighting of the light source can be suppressed as low aspossible. Besides, since the smooth curve with less irregularity can beobtained, it is natural that the light emission spectrum of blackbodyradiation can easily be reproduced and the color rendering property orthe like can be improved. In particular, the light sources of thepresent invention are characterized in that the light emission intensitydoes not become zero even in a near-ultraviolet region of 380 nm or adeep red region of 780 nm. On the other hand, in the light source ofFIG. 17 of the Comparative Example, planar curves appear in a region of400 nm or less and in a region of 750 nm or more, and the level of theintensity thereof can be regarded as substantially zero. Thus, in thewhite light source of the present invention, over the entire wavelengthregion of 380 nm to 780 nm which is the object of evaluation of thecolor rendering evaluation index, there is no planar wavelength regionin which the light emission intensity is substantially zero.Accordingly, the white light source of the present invention can exhibithigh numerical values, not only with respect to the average index Ra,but also with respect to R₁ to R₁₅. Concrete values are as shown inTable 9. FIG. 18 to FIG. 20 show other examples of continuous spectrawith no break over the entire wavelength range of 380 nm to 780 nm, thatis, light emission spectra including no planar wavelength region inwhich the emission intensity is substantially zero.

TABLE 9 Light source Ra R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14R15 Light source 7  95.1 91.7 94.2 96.2 91.7 90.8 92.0 96.9 88.6 85.185.7 90.4 85.9 92.0 97.6 89.0 Light source 8  96.9 96.4 97.7 98.8 96.396.1 96.7 98.2 94.6 85.0 94.5 96.4 88.7 96.7 99.3 94.8 Light source 9 95.2 90.5 93.4 98.9 93.1 91.7 92.1 97.6 92.0 85.2 97.9 90.7 87.2 90.698.4 88.4 Light source 10 95.4 93.1 95.3 99.1 94.8 93.8 93.7 98.4 94.885.0 91.2 92.6 90.0 93.1 98.8 92.2 Light source 11 98.1 98.8 98.8 99.996.8 97.8 98.1 97.0 97.5 98.5 98.5 99.2 85.8 98.2 99.4 96.6

As regards the white light sources 7 to 12, movements on the u′v′chromaticity diagram were measured and evaluated with respect to thelight emission color variations during continuous lighting. Aftermeasuring the light emission spectra of the white light sources 7 to 12by using an integrating sphere, chromaticity values of u′ and v′ wereobtained by calculation. One hour after the time of initial lighting, u′and v′ were measured. Then, after continuous lighting of 6000 hoursthereafter, u′ and v′ at the time point of the lapse of 6000 hours weremeasured. Incidentally, the measurement was conducted in an indoorenvironment at a room temperature of 25° C. and with a humidity of 60%.From the (u′, v′) after one hour and the (u′, v′) after the lapse of6000 hours, differences Δu′ and Δv′ therebetween were found, and themagnitude of the chromaticity variation was calculated as[(Δu′)²+(Δv′)²]^(1/2). The result is shown in Table 10.

TABLE 10 Magnitude of chromaticity Light sources variation: [(Δu′)² +(Δv′)²]^(1/2) Light source 7 Example A 0.006 Light source 8 Example A0.007 Light source 9 Example A 0.006 Light source 10 Example A 0.008Light source 11 Example A 0.009 Light source 12 Comparative 0.017Example

In the Table, the white light source 12 is a light source of theComparative Example, which was experimentally fabricated for the purposeof comparison of characteristics. The basic configuration of the LEDmodule is the same as that of the light sources 7 to 10 of Example A.However, InGaN having a light emission peak at 455 nm was used for theLED, and a cerium activated yttrium aluminum garnet phosphor was used asa phosphor to be combined. Besides, the thickness of the phosphor layerand the amount of phosphor were adjusted such that white light of acolor temperature of 5300 K is emitted from the light source 12 of theComparative Example. Concretely, the film thickness was set at 0.15 mm,and the content of phosphor powder in the phosphor layer was set at 10mass %.

In the light source 12 of the Comparative Example, the chromaticityvariation after continuous lighting exceeded 0.01 and was large.Although the white light of the light source 12 is obtained by themixing the blue light of the LED and the yellow light of the phosphor,the speed of the decrease in luminance of the LED and the speed of thedecrease in luminance of the phosphor during continuous lighting aredifferent, and thus such a large variation was exhibited. On the otherhand, in the white light sources 7 to 11 of the present invention, allthe constituent components of the white light utilize the emissionlights of phosphors, and the phosphors used are doubly excited by theLED and phosphors. Moreover, the combination in which re-absorptionbetween the phosphors occurs is adopted. Thus, the speeds of thedecrease of luminance in the respective phosphors are averaged. As aresult, the effect of reduction of the color variation was broughtabout. In the white light sources of the present invention, themagnitude of the chromaticity variation in each light source was 0.01 orless, and was small.

Example B

White light sources were fabricated in order to examine the relationshipbetween the water absorption coefficient of the alumina substrate andthe adhesion strength of the silicone resin. Except for the material ofthe substrate, use was made of the same members for fabricating thelight sources as those of the light source 7 of Example A. The basicconfiguration of the LED module was also the same as that of the lightsource 7. However, in order to evaluate the strength of the resin film,the configuration was simplified, and a linear arrangement of only onecolumn was adopted as the chip arrangement of LEDs, instead of thematrix-type arrangement.

As a substrate of a light source 13, an alumina substrate (shape:8×3×0.38 mm) with a water absorption coefficient of 5.8% was prepared.The temperature at a time of baking this alumina substrate was set at1480° C., and thereby the water absorption coefficient was adjusted to5.8%. Three LED chips were linearly arranged on this substrate, and wereconnected in series. A slurry including four kinds of phosphors andsilicone resin was applied onto these LED chips such that the three LEDchips were covered at the same time, and the silicone resin was cured bya heat treatment at a temperature of 140° C. In this manner, a columnarphosphor layer was formed with a size of 6.5 mm in longitudinaldimension, 2.5 mm in transverse dimension, and 1.9 mm in thickness.

As substrates of light sources 14 and 15, alumina substrates havingwater absorption coefficients of 38% and 59%, respectively, wereprepared, and the same LED modules as in the light source 13 werefabricated.

In addition, as a light source 16, an LED module having a double-layerstructure of a transparent silicone resin layer and a phosphor layer wasfabricated. Three LED chips were mounted on an alumina substrate havinga water absorption coefficient of 11%. Thereafter, a silicone resinincluding no phosphor was applied. Next, a phosphor slurry prepared forthe light source 13 was applied. The resultant was subjected to heattreatment at a temperature of 140° C., and the silicone resin was cured.Thereby, a double-layer film was formed in which the thickness of thetransparent silicone resin layer is 3 mm and the thickness of thephosphor layer is 0.5 mm.

As a light source 17, a module to be described below was fabricated. Themodule was fabricated by the same method as the light source 13, exceptthat an alumina substrate having a water absorption coefficient of 0%was used as the substrate material. An electric current of 20 mA waspassed through the above five kinds of white light sources 13 to 17 andthe light source 10 of Example A, and the light emission efficiency ofeach light source was measured. Thereafter, the adhesion strengthbetween the silicone resin and substrate was measured by a predeterminedmethod. The result is shown in Table 11. In the light source 10 ofExample A and the light sources 13 to 16 of Example B in which thealumina substrates having the water absorption coefficients in the rangeof 5% to 60% were used, the adhesion strength between the silicone resinlayer and substrate indicated a characteristic of more than 1 N, andlight sources with no peeling of the resin layer and with good handlingefficiency were successfully obtained.

TABLE 11 Water absorption Structure Adhesion Light emission coefficientof strength efficiency of substrate Resin layer (N) (lm/W) Light source10 21 Double-layer film 5.9 65 (Example A) Light source 13 5.8Single-layer film 4.1 60 (Example B) Light source 14 38 Single-layerfilm 7.2 59 (Example B) Light source 15 59 Single-layer film 8.8 61(Example B) Light source 16 11 Double-layer film 5.1 64 (Example B)Light source 17 0 Single-layer film 0.5 59 (Example B)

Example C

White light sources were fabricated for confirming the characteristiceffect of the transparent resin layer that is a constituent member of anLED module, and characteristic effect of inorganic fine particle powderincluded in the transparent resin layer.

To begin with, the effects of the transparent resin layers wereevaluated. The members used for fabricating the light sources wereexactly the same as those in the light source 7 of Example A. As regardsthe arrangement of LEDs, substrate shape and transparent resin layer,unique configurations were adopted for the purpose of evaluation.

In a light source 18, three violet light emission LED chips (GaN) weredie-bonded to an alumina substrate (8.0 mm in longitudinal dimension×3.0mm in transverse dimension) including a wiring pattern electrode, by asolder paste or the like at intervals of 2.0 mm. The bonded LED chipswere wire-bonded to the wiring pattern by using gold wires. Afterconfirming the lighting of the LEDs, the LEDs and gold wires were coatedwith a thermosetting transparent silicone resin. In the method ofcoating, a necessary amount of the resin was applied by using adispenser, a mask or the like, such that the center LED chip is set atthe center, and the three LEDs are coated with a common continuoustransparent resin layer. The resin was heated and cured at temperaturesof 100 to 150° C., and thus the transparent resin layer was formed. Thesize of the transparent resin layer was 5.5 mm in longitudinaldimension×2.5 mm in transverse dimension, and the thickness thereof was1.2 mm. Next, a silicone resin including a phosphor was applied to thesurface of the transparent resin layer, and heated and cured. Thereby, aphosphor layer (7.5 mm in longitudinal dimension×3.0 mm in transversedimension×1.5 mm in thickness) was formed, and the LED module of ExampleC was fabricated.

As regards a light source 19, a light source having exactly the sameconfiguration as the light source 18, except for the transparent resinlayer, was fabricated. As regards the transparent resin layer, the threeLED chips were not coated with the continuous transparent resin layer.Instead, each of the LED chips was coated with an individual independenttransparent resin layer. As regards the phosphor layer, the threetransparent resin films were coated with an identical continuousphosphor layer, and the same phosphor layer (7.5 mm in longitudinaldimension×3.0 mm in transverse dimension×1.5 mm in thickness) as in thelight source 18 was formed.

A light source 20 was fabricated. The light source 20 was formed withthe same configuration as the light source 18 and light source 19.However, the transparent resin layer was not formed between the LED andthe phosphor layer.

The above three kinds of light sources and the light source 10 ofExample A were evaluated in the following procedure. As shown in FIG.43, nine measurement points A to I on a phosphor layer 84 weredetermined, and the luminances on the respective measurement points weremeasured by a two-dimensional color/luminance analyzer CA-2000(manufactured by KONICA MINOLTA JAPAN, INC.). From the measured valuesof the luminance at the respective measurement points, the nonuniformityin luminance of each semiconductor light emission device was evaluated.The result is as shown in Table 12. Numerical values in the Table areluminance (Cd/m²), and numerical values in parentheses ( ) are relativevalues in the case in which the luminance at point E was set as 100. Ifthe luminance at the center point E and the luminances at thesurrounding points are compared, it is understood that the difference inluminance between the central part and the surrounding part in eachExample is small, and that the light emitting devices of Example A andExample C have substantially uniform luminance characteristics.

TABLE 12 Measurement points A B C D E F G H I Light source 10 30715310595 30369 33131 34511 33476 29334 31060 30025 Example A (89) (90)(88) (96) (100) (97) (85) (90) (87) Light source 18 26961 28529 2727530723 31350 31073 27275 28529 27275 Example C (86) (91) (87) (98) (100)(99) (87) (91) (87) Light source 19 26926 27591 25596 30915 33242 3058327258 27257 26594 Example C (81) (83) (77) (93) (100) (92) (82) (82)(80) Light source 20 20324 21001 21340 30824 38873 30819 21679 2133920662 Example C (60) (62) (63) (91) (100) (91) (64) (63) (61)

Example D

The kinds of inorganic fine particle powder dispersed in transparentresin layers were evaluated. The evaluation was conducted by fabricatinglight sources in which various kinds of inorganic fine particle powderwere disposed in transparent resin layers, and by measuring the lightemission efficiencies of the obtained light sources. The light emissionefficiencies were measured by using an integrating sphere manufacturedby Labsphere, Inc. Incidentally, in the light sources 21 to 25, thedevice configuration of the LEDs was identical to that of the lightsource 18 of Example C, except for the presence/absence of inorganicfine particle powder in the transparent resin layer. The result is shownin Table 13. Table 13 also shows the result relating to the light source10 of Example A.

As is clear from Table 13, the light emission efficiency is excellent inthe light source 10 of Example A and light sources 21 to 23 of Example Dwhich use inorganic fine particle powder with a maximum particle size of¼ or less of the light emission peak wavelength (405 nm) of the LEDchip, compared to the light sources 24 and 25 of Example D which useinorganic fine particle powder with a maximum particle size of more than¼ of the light emission peak wavelength (405 nm) of the LED chip. Inparticular, the light source 10 and light source 21, which use fumedsilica with a maximum particle size of 25 μm, exhibited excellentcharacteristics.

TABLE 13 Inorganic fine particle powder Average primary Maximum Lightparticle particle emission kind of size size Content efficiency material(μm) (μm) (mass %) (lm/W) Light source 10 Fumed 7 25 3 65.0 (Example A)silica Light source 21 Fumed 7 25 3 67.0 (Example D) silica Light source22 Colloidal 48 79 3 64.5 (Example D) silica Light source 23 Fumed 30 773 65.1 (Example D) alumina Light source 24 Colloidal 101 125 3 52.1(Example D) silica Light source 25 Pulverized 210 545 3 49.3 (Example D)alumina

Example E

Finally, as regards the inorganic fine particle powder in thetransparent resin layer, the optimal content was confirmed. In theevaluation, use was made of light sources in which the contents of,mainly, fumed silica that exhibits most excellent characteristics werevaried. The detailed configuration of the light sources is identical tothat of the light sources 21 and 23, except that the content ofinorganic fine particle powder was varied. The result is as shown inTable 14. Table 14 also shows the result relating to the light source 10of Example A. By dispersing the inorganic fine particle powder in thetransparent resin layer, the light emission efficiency of the lightsource can be enhanced. A preferable content of inorganic fine particlepowder was 0.1 mass % to 5 mass %, and a more preferable content was 1mass % to 5 mass %.

TABLE 14 Material kind of Light emission inorganic fine Contentefficiency particle powder (mass %) (lm/W) Light source 10 Fumed silica3.0 65.0 (Example A) Light source 26 Fumed silica 0.06 53.5 (lightsource 21 of Example E) Light source 27 Fumed alumina 0.08 52.9 (lightsource 23 of Example E) Light source 28 Fumed silica 1.0 63.9 (lightsource 21 of Example E) Light source 29 Fumed alumina 1.0 62.7 (lightsource 23 of Example E) Light source 30 Fumed silica 2.0 65.5 (lightsource 21 of Example E) Light source 31 Fumed silica 3.5 66.8 (lightsource 21 of Example E) Light source 32 Fumed silica 4.8 65.8 (lightsource 21 of Example E) Light source 33 Fumed silica 6.0 55.9 (lightsource 21 of Example E) Light source 34 — 0 52.5 (light source 21 ofExample E)

Examples 3 to 7

A white light source system of the present invention, which canreproduce various correlated color temperatures, was fabricated byarbitrarily mixing lights from at least two kinds of light sourcesselected from among the white light sources 1 to 6 described in Table1-2 of Example 1. This system can reproduce all chromaticity points in ahexagonal inside area formed by six light emission chromaticity pointsindicated by the respective light sources. Thus, over all colortemperatures of 2000 K to 6500 K, the system can reproduce allcorrelated chromaticity points in the range of ±0.005 duv or less. Inaddition, the same light source as in Example 1 is used for each lightsource, and it is natural that the white light reproduced by this whitelight source system can exhibit the same characteristics as the otherExamples, that is, the characteristics such as the color renderingproperty and light emission spectrum shape.

In Examples 3 to 7, one-day variations of sunlight in various placeswere reproduced by using this white light source system. The variationsof the correlated color temperature and illuminance in the respectiveplaces are as shown in FIG. 22 to FIG. 26

Example 3: one-day variations of sunlight in spring in Wakkanai(Hokkaido), Japan.

Example 4: one-day variations of sunlight in summer in Taipei, Taiwan.

Example 5: one-day variations of sunlight in summer in Los Angeles, theUSA.

Example 6: one-day variations of sunlight in autumn in Sakai (Osaka),Japan.

Example 7: one-day variations of sunlight in winter in Naha (Okinawa),Japan.

In the above description, only the variations of sunlight in some placeson the earth were reproduced. However, from the data stored in thesystem, the user may designate data of sunlight of an arbitrary seasonat an arbitrary place. Thereby, the variations of sunlight in suchplaces can be well reproduced. Specifically, the light emission spectrumof the white light source of the present invention can exhibit goodcoincidence in the visible light region with the light emission spectrumof blackbody radiation of the same color temperature as sunlight.Moreover, the spectrum shape of the blackbody radiation is not merelyreproduced, but the degree of influence, which light emission byblackbody radiation (sun) receives while reaching each place on theearth, is quantized as a deviation from the color temperature ofblackbody radiation. Thus, the white light of the color temperature,with this deviation being included, was successfully reproduced.Thereby, the sunlight in an arbitrary place can be reproduced, and thereproduced light contains only ultraviolet which is much weaker thansunlight. Hence, for example, when the reproduced light is used asillumination for articles on exhibition in an art museum or the like,paintings or the like are not damaged, and the real body colors of thearticles on exhibition can be reproduced with very high precision,compared to conventional light sources. Furthermore, the white lightsource of the present invention can serve as a light source that is kindto human bodies. This light source can radiate white light in which theintensity of the blue light emission component that is a concern due toits harmful effect on paintings and human bodies is sufficientlyreduced, compared to conventional artificial light sources, and thislight source can well maintain the circadian rhythms of human bodies andbe good for human bodies, while being able to obtain a high colorrendering effect, like sunlight.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. An indoor light comprising, a substrate; LED chips arranged on thesubstrate at intervals with each other; a phosphor layer directly orindirectly covering a periphery of the LED chips and containing asilicone resin and phosphors each having a peak wavelength of a lightemission spectrum; and a cover fixed to the substrate, wherein mutualabsorption occurs in the phosphors, and wherein P(λ), B(λ) and V(λ)satisfy equation (1) below in a wavelength range in which λ is 380 nm to780 nm, and the indoor light satisfies expression (5) below in awavelength range of 400 nm to 495 nm: $\begin{matrix}{{\int_{380}^{780}{{P(\lambda)}{V(\lambda)}d\;\lambda}} = {\int_{380}^{780}{{B(\lambda)}{V(\lambda)}d\;\lambda}}} & (1)\end{matrix}$wherein P(λ)/B(λ)≤1.5   (5) wherein P(λ) is a light emission spectrum ofthe white light emitted from the indoor light, B(λ) is a light emissionspectrum of blackbody radiation of a color temperature correspond to acolor temperature of the white light, and V(λ) is a spectrum of aspectral luminous efficiency, and wherein a chromaticity variation ofthe indoor light after continuous lighting of 6000 hours is expressed asa variation of chromaticity on a CIE chromaticity diagram, and 0.01 orless.
 2. The indoor light of claim 1, wherein the indoor light isconfigured to be capable of reproducing white light of a colortemperature of 2000 K to 6500 K on a locus of the blackbody radiation,and white light of any one of correlated color temperatures with adeviation from the color temperature of the white light being in a rangeof ±0.005 duv.
 3. The indoor light of claim 2, wherein an intervalbetween each peak wavelength and a neighboring peak wavelength is 150 nmor less.
 4. The indoor light of claim 2, wherein the phosphors eachexhibits a light emission spectrum having a half-value width of 50 nm ormore.
 5. The indoor light of claim 2, wherein light emission spectra ofthe respective phosphors have different peak wavelengths, and include atleast one wavelength region where a part of each light emission spectrumoverlaps another light emission spectrum.
 6. The indoor light of claim2, wherein the phosphors are a mixture of at least three kinds ofphosphors selected from the group consisting of a blue phosphor, a greenphosphor, a yellow phosphor and a red phosphor.
 7. The indoor light ofclaim 6, wherein the mixture of phosphors comprises a blue-greenphosphor.
 8. The indoor light of claim 6, wherein the blue phosphor isat least one kind selected from between a europium activated strontiumaluminate phosphor having a light emission peak wavelength of 480 to 500nm, and a europium activated alkaline earth phosphate phosphor having alight emission peak wavelength of 440 to 460 nm.
 9. The indoor light ofclaim 6, wherein the green phosphor is at least one kind selected fromamong a europium activated orthosilicate phosphor having a lightemission peak wavelength of 520 to 550 nm, a europium activated β-sialonphosphor having a light emission peak wavelength of 535 to 545 nm, and aeuropium activated strontium sialon phosphor having a light emissionpeak wavelength of 520 to 540 nm.
 10. The indoor light of claim 6,wherein the yellow phosphor is at least one kind selected from between aeuropium activated orthosilicate phosphor having a light emission peakwavelength of 550 to 580 nm, and a cerium activated rare earth aluminumgarnet phosphor having a light emission peak wavelength of 550 to 580nm.
 11. The indoor light of claim 6, wherein the red phosphor is atleast one kind selected from among a europium activated strontium sialonphosphor having a light emission peak wavelength of 600 to 630 nm, aeuropium activated calcium nitridoaluminosilicate phosphor having alight emission peak wavelength of 620 to 660 nm, and a manganeseactivated magnesium fluorogermanate phosphor having a light emissionpeak wavelength of 640 to 660 nm.
 12. The indoor light of claim 1,wherein an average color rendering index Ra of the white light emittedfrom the indoor light is 95 or more, and all of color rendering indexesR₁ to R₈ and special color rendering indexes R₉ to R₁₅ are 85 or more.13. The indoor light of claim 12, wherein the average color renderingindex Ra of the white light emitted from the indoor light is 97 or more,and all of the color rendering indexes R₁ to R₈ and the special colorrendering indexes R₉ to R₁₅ are 90 or more.
 14. The indoor light ofclaim 1, wherein the phosphors are a mixture of at least three kinds ofphosphors selected from the group consisting of a blue phosphor, ablue-green phosphor, a green phosphor, a yellow phosphor and a redphosphor, and wherein the green phosphor and/or the yellow phosphor is aeuropium activated orthosilicate phosphor.
 15. The indoor light of claim1, which is used for a home, an office, a hospital or an art museum.